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Variation in the Muscles and Nerves of the Leg in Two Genera of Grouse (Tympanuchus and Pedioecetes)

by E. Bruce Holmes · English · Gutenberg #41812 · 324,997 chars · public domain (US)

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Title: Variation in the Muscles and Nerves of the Leg in Two Genera of Grouse (Tympanuchus and Pedioecetes)

Author: E. Bruce Holmes


        
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*** START OF THE PROJECT GUTENBERG EBOOK VARIATION IN THE MUSCLES AND NERVES OF THE LEG IN TWO GENERA OF GROUSE (TYMPANUCHUS AND PEDIOECETES) ***

          UNIVERSITY OF KANSAS PUBLICATIONS
              MUSEUM OF NATURAL HISTORY

        Vol. 12, No. 9, pp. 363-474, 20 figs.

                   October 25, 1963


         Variation in the Muscles and Nerves
         of the Leg in Two Genera of Grouse
            (Tympanuchus and Pedioecetes)

                          BY
                   E. BRUCE HOLMES



                UNIVERSITY OF KANSAS
                       LAWRENCE
                         1963




UNIVERSITY OF KANSAS PUBLICATIONS
MUSEUM OF NATURAL HISTORY


Institutional libraries interested in publications exchange may obtain
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  * An asterisk designates those numbers of which the Museum's supply (not
    the Library's supply) is exhausted. Numbers published to date, in this
    series, are as follows:

   Vol.  1.  Nos. 1-26 and index. Pp. 1-638, 1946-1950.

  *Vol.  2. (Complete) Mammals of Washington. By Walter W. Dalquest. Pp.
               1-444, 140 figures in text. April 9, 1948.

   Vol.  3. *1. The avifauna of Micronesia, its origin, evolution, and
                distribution. By Rollin H. Baker. Pp. 1-359, 16 figures
                in text. June 12, 1951.

            *2. A quantitative study of the nocturnal migration of birds.
                By George H. Lowery, Jr. Pp. 361-472, 47 figures in text.
                June 29, 1951.

             3. Phylogeny of the waxwings and allied birds. By M. Dale
                Arvey. Pp. 473-530, 49 figures in text, 13 tables.
                October 10, 1951.

            *4. Birds from the state of Veracruz, Mexico. By George H.
                Lowery, Jr., and Walter W. Dalquest. Pp. 531-649, 7
                figures in text, 2 tables. October 10, 1951.

             Index. Pp. 651-681.

  *Vol.  4. (Complete) American weasels. By E. Raymond Hall. Pp. 1-466,
            41 plates, 31 figures in text. December 27, 1951.

   Vol.  5. Nos. 1-37 and index. Pp. 1-676, 1951-1953.

  *Vol.  6. (Complete) Mammals of Utah, _taxonomy and distribution_. By
            Stephen D. Durrant. Pp. 1-549, 91 figures in text, 30 tables.
            August 10, 1952.

   Vol.  7. Nos. 1-15 and index. Pp. 1-651, 1952-1955.

   Vol.  8. Nos. 1-10 and index. Pp. 1-675, 1954-1956.

   Vol.  9. *1. Speciation of the wandering shrew. By James S. Findley.
                Pp. 1-68, 18 figures in text. December 10, 1955.

             2. Additional records and extension of ranges of mammals
                from Utah. By Stephen D. Durrant, M. Raymond Lee, and
                Richard M. Hansen, Pp. 69-80. December 10, 1955.

             3. A new long-eared myotis (Myotis evotis) from
                northeastern Mexico. By Rollin H. Baker and Howard J.
                Stains. Pp. 81-84. December 10, 1955.

             4. Subspeciation in the meadow mouse, Microtus
                pennsylvanicus, in Wyoming. By Sydney Anderson. Pp.
                85-104, 2 figures in text. May 10, 1956.

             5. The condylarth genus Ellipsodon. By Robert W. Wilson.
                Pp. 105-116, 6 figures in text. May 19, 1956.

             6. Additional remains of the multituberculate genus
                Eucosmodon. By Robert W. Wilson. Pp. 117-123, 10 figures
                in text. May 19, 1956.

             7. Mammals of Coahulia, Mexico. By Rollin H. Baker. Pp.
                125-335, 75 figures in text. June 15, 1956.

             8. Comments on the taxonomic status of Apodemus peninsulae,
                with description of a new subspecies from North China.
                By J. Knox Jones, Jr. Pp. 337-346, 1 figure in text, 1
                table. August 15, 1956.

             9. Extensions of known ranges of Mexican bats. By Sydney
                Anderson. Pp. 347-351. August 15, 1956.

            10. A new bat (Genus Leptonycteris) from Coahulia. By Howard
                J. Stains. Pp. 353-356. January 21, 1957.

            11. A new species of pocket gopher (Genus Pappogeomys) from
                Jalisco, Mexico. By Robert J. Russell. Pp. 357-361.
                January 21, 1957.

            12. Geographic variation in the pocket gopher, Thomomys
                bottae, in Colorado. By Phillip M. Youngman. Pp. 363-384,
                7 figures in text. February 21, 1958.

            13. New bog lemming (genus Synaptomys) from Nebraska. By J.
                Knox Jones, Jr. Pp. 385-388. May 12, 1958.

            14. Pleistocene bats from San Josecito Cave, Nuevo León,
                México. By J. Knox Jones, Jr. Pp. 389-396. December 19,
                1958.

            15. New subspecies of the rodent Baiomys from Central
                America. By Robert L. Packard. Pp. 397-404. December 19,
                1958.

            16. Mammals of the Grand Mesa, Colorado. By Sydney Anderson.
                Pp. 405-414, 1 figure in text. May 20, 1959.

            17. Distribution, variation, and relationships of the montane
                vole, Microtus montanus. By Sydney Anderson. Pp. 415-511,
                12 figures in text, 2 tables. August 1, 1959.

      (Continued on inside of back cover)




              UNIVERSITY OF KANSAS PUBLICATIONS
                  MUSEUM OF NATURAL HISTORY

             Vol. 12, No. 9, pp. 363-474, 20 figs.

                      October 25, 1963

              Variation in the Muscles and Nerves
              of the Leg in Two Genera of Grouse
                 (Tympanuchus and Pedioecetes)

                              BY
                       E. BRUCE HOLMES

                    UNIVERSITY OF KANSAS
                          LAWRENCE
                            1963




UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

     Editors: E. Raymond Hall, Chairman, Henry S. Fitch,
                    Theodore H. Eaton, Jr.


           Volume 12, No. 9, pp. 363-474, 20 figs.
                 Published October 25, 1963


                    UNIVERSITY OF KANSAS
                      Lawrence, Kansas


                         PRINTED BY
             JEAN M. NEIBARGER, STATE PRINTER
                       TOPEKA, KANSAS
                            1963

                       [Illustration]

                           29-5835




            Variation in the Muscles and Nerves
            of the Leg in Two Genera of Grouse
               (Tympanuchus and Pedioecetes)

                             BY

                       E. BRUCE HOLMES




CONTENTS


                                                     PAGE

  Introduction                                        367

  Materials and Methods                               368

  Terminology                                         369

  Acknowledgments                                     375

  Skeleton                                            375

  Nerves                                              376
    Lumbosacral Plexus                                376
    Femoral Nerve                                     377
    Obturator Nerve                                   379
    Sciatic Nerve                                     379
    Peroneal Nerve                                    382
    Tibial Nerve                                      384

  Muscles                                             396
    M. Extensor Iliotibialis Lateralis                398
    M. Extensor Iliotibialis Anticus                  405
    M. Ambiens                                        408
    M. Vastus Lateralis                               408
    M. Vastus Medialis                                410
    M. Femoritibialis Internus                        410
    M. Extensor Iliofibularis                         411
    M. Piriformis                                     412
    M. Gluteus Profundus                              413
    M. Iliacus                                        414
    M. Iliotrochantericus Medius                      415
    M. Psoas                                          416
    M. Flexor Cruris Lateralis                        416
    M. Flexor Cruris Medialis                         417
    M. Caudofemoralis                                 418
    M. Flexor Ischiofemoralis                         420
    M. Adductor Superficialis                         420
    M. Adductor Profundus                             421
    M. Obturator                                      422
    M. Femorocruralis                                 425
    M. Gastrocnemius                                  426
    M. Flexor Perforans et Perforatus Digiti II       427
    M. Flexor Perforans et Perforatus Digiti III      429
    M. Flexor Perforatus Digiti IV                    430
    M. Flexor Perforatus Digiti III                   432
    M. Flexor Perforatus Digiti II                    433
    M. Flexor Hallucis Longus                         435
    M. Plantaris                                      435
    M. Flexor Digitorum Longus                        436
    M. Popliteus                                      438
    M. Peroneus Longus                                438
    M. Tibialis Anticus                               439
    M. Extensor Digitorum Longus                      440
    M. Peroneus Brevis                                441
    M. Extensor Hallucis Longus                       442
    M. Abductor Digiti II                             443
    M. Extensor Brevis Digiti III                     444
    M. Extensor Proprius Digiti III                   444
    M. Extensor Brevis Digiti IV                      445
    M. Lumbricalis                                    445
    M. Abductor Digiti IV                             446
    M. Flexor Hallucis Brevis                         446

  Discussion and Conclusions                          446
    Analysis of Individual Variation                  446
      Muscles                                         447
      Nerves                                          449
    Analysis of Variation Between Species             451
    Comparison with Other Studies of Innervation      452

  Summary                                             457

  Literature Cited                                    473




LIST OF ILLUSTRATIONS


                                                                       PAGE


  FIG. 1. Pelvis of _Tympanuchus pallidicinctus_.
    A. Lateral view. × 1. B. Ventral view. × 1-1/8.                     370

  FIG. 2. Ventral views of the lumbosacral plexus of
    _Tympanuchus pallidicinctus_.
    Sympathetic ganglionated chain removed. Numbers indicate
    synsacral spinal nerves. × 2. A. T.p. 1L. B. T.p. 2L.               386

  FIG. 3. Ventral views of the lumbosacral plexus.
    Sympathetic ganglionated chain removed. Numbers indicate
    synsacral spinal nerves. × 2. A. _Tympanuchus cupido pinnatus_
    3L. B. _Pedioecetes phasianellus jamesi_ 4L.                        387

  FIG. 4. Semidiagrammatic ventral views of the femoral
    nerve, showing the distribution of the branches. × 3. 1,2,
    M. extensor iliotibialis anticus; 3, cutaneous; 4-6, M. extensor
    iliotibialis lateralis; 7,8, M. iliacus; 9, M. gluteus
    profundus; 10-12, fused Mm. vastus lateralis and vastus
    medialis; 13,14, M. vastus medialis; 15, M. ambiens;
    16, M. femoritibialis internus; 17, nonmuscular; 18, M.
    psoas; 19, M. iliotrochantericus medius. A. _Tympanuchus
    cupido pinnatus_ 3L. B. _Pedioecetes phasianellus
    jamesi_ 3L.                                                         388

  FIG. 5. Semidiagrammatic ventral views of the femoral
    nerve, showing the distribution of the branches. × 3. 1,2, M.
    extensor iliotibialis anticus; 3, cutaneous; 5,6, M. extensor
    iliotibialis lateralis; 7,8, M. iliacus; 9, M. gluteus
    profundus; 10,11, fused Mm. vastus lateralis and vastus
    medialis; 13, M. vastus medialis; 15, M. ambiens; 16,
    M. femoritibialis internus; 17, nonmuscular; 18, M. psoas;
    19, M. iliotrochantericus medius. A. _Tympanuchus
    pallidicinctus_ 2L. B. _Tympanuchus cupido attwateri_ 1R.           389

  FIG. 6. Semidiagrammatic dorsolateral view of the sciatic
    nerve of _Pedioecetes phasianellus jamesi_ 3R, showing
    the distribution of the branches. × 2-1/2. 1, M. gluteus
    profundus; 2, M. piriformis; 3, M. extensor iliotibialis
    lateralis; 4-7, M. extensor iliofibularis; 8, M. flexor cruris
    medialis; 9, cutaneous; 10, to pudendal plexus; 11, M. flexor
    cruris lateralis; 12, M. caudofemoralis pars caudifemoralis;
    13-15, M. caudofemoralis pars iliofemoralis; 16,17, M. flexor
    ischiofemoralis; 18,19, M. femorocruralis (branch of tibial
    nerve); 20, cutaneous; 21, M. gastrocnemius pars media (branch
    of tibial nerve); 22, cutaneous.                                    390

  FIG. 7. Semidiagrammatic dorsolateral view of the sciatic
    nerve of _Tympanuchus pallidicinctus_ 2L, showing the
    distribution of the branches. × 2-1/2. 1, M. gluteus profundus;
    2, M. piriformis; 3, M. extensor iliotibialis lateralis; 4, 7,
    M. extensor iliofibularis; 8, M. flexor cruris medialis; 9,
    cutaneous; 10, to pudendal plexus; 11, M. flexor cruris
    lateralis; 12, M. caudofemoralis pars caudifemoralis; 13-15,
    M. caudofemoralis pars iliofemoralis; 17, M. flexor
    ischiofemoralis; 18, M. femorocruralis (branch of tibial nerve);
    22, cutaneous; 23, nonmuscular (branch of peroneal nerve).          391

  FIG. 8. Semidiagrammatic dorsolateral view of the
    sciatic nerve of _Tympanuchus cupido pinnatus_ 3L,
    showing the distribution of the branches. × 2-1/2. 1,
    M. gluteus profundus; 2, M. piriformis; 3, M. extensor
    iliotibialis lateralis; 4,7, M. extensor iliofibularis;
    8, M. flexor cruris medialis; 9, cutaneous; 11, M. flexor
    cruris lateralis; 12, M. caudofemoralis pars caudifemoralis;
    13, M. caudofemoralis pars iliofemoralis; 17, M. flexor
    ischiofemoralis; 18, M. femorocruralis (branch of tibial
    nerve); 20, cutaneous; 22, cutaneous.                               392

  FIG. 9. Semidiagrammatic dorsolateral view of the
    sciatic nerve of _Pedioecetes phasianellus jamesi_ 3L,
    showing the distribution of the branches. × 2-1/2. 1,
    M. gluteus profundus; 2, M. piriformis; 3, M. extensor
    iliotibialis lateralis; 4,5,7, M. extensor iliofibularis;
    8, M. flexor cruris medialis; 9, cutaneous; 11, M. flexor
    cruris lateralis; 13,14, M. caudofemoralis pars iliofemoralis;
    16,17, M. flexor ischiofemoralis; 18,19, M. femorocruralis
    (branch of tibial nerve); 20, cutaneous; 22, cutaneous.             393

  FIG. 10. A,B. Semidiagrammatic drawings of the peroneal
    nerve of _Tympanuchus pallidicinctus_ 1L, showing the
    distribution of the branches. × 2. C. Semidiagrammatic drawing
    of the distal part of the peroneal nerve of _Tympanuchus
    cupido attwateri_ 1R, showing the distribution of the
    branches. × 2. 1,2, M. tibialis anticus (tibial head); 3,4,
    M. tibialis anticus (femoral head); 5, M. extensor digitorum
    longus; 6, nonmuscular; 7,8, M. peroneus longus; 9, M. peroneus
    brevis; 10,11, M. extensor hallucis longus (proximal head);
    12, M. extensor hallucis longus (distal head); 13-15, nonmuscular
    (to toes); 16, M. abductor digiti II; 17, M. extensor brevis
    digiti III; 18, M. extensor brevis digiti IV.                       394

  FIG. 11. A,B. Semidiagrammatic drawings of the tibial
    nerve (excluding the paraperoneal branch) of _Tympanuchus
    pallidicinctus_, showing the distribution of the branches.
    × 2. A. T.p. 1L. B. T.p. 3R. C. Semidiagrammatic drawing
    of the distal part of the paraperoneal branch of the tibial
    nerve of _Pedioecetes phasianellus jamesi_ 2L, showing
    the distribution of the branches. × 2. 1, M. femorocruralis;
    2, M. gastrocnemius pars media; 3, M. popliteus; 4, M. plantaris;
    5, M. flexor digitorum longus; 6-8, nonmuscular; 9-11, M.
    gastrocnemius pars interna; 12,13, M. flexor hallucis longus;
    14-16, M. flexor perforatus digiti IV (medial head); 17, M.
    flexor perforatus digiti III (medial head); 18-20, M. flexor
    perforatus digiti II; 21, M. flexor perforatus digiti IV
    (lateral head); 22-24, M. flexor perforatus digiti IV
    (anterolateral head); 25, M. flexor perforatus digiti III
    (anterolateral head); 26, M. flexor perforans et perforatus
    digiti III; 27,28, M. flexor perforans et perforatus digiti II;
    29, M. gastrocnemius pars externa; 30,31, M. abductor digiti IV;
    32,33, M. flexor hallucis brevis; 34,35, nonmuscular (to toes).     395

  FIG. 12. _Tympanuchus pallidicinctus_ 2L. Lateral
    view of the superficial muscles of the left leg. × 1.               397

  FIG. 13. _Tympanuchus pallidicinctus_ 2L. Medial
    view of the superficial muscles of the left leg. × 1. Articular
    capsule shown by concentrically arranged dashes.                    398

  FIG. 14. _Tympanuchus pallidicinctus_ 2L. Lateral
    view of the muscles of the left leg. The following muscles have
    been removed: extensor iliotibialis lateralis, extensor
    iliotibialis anticus, gastrocnemius pars externa and pars
    interna, and peroneus longus. × 1.                                  399

  FIG. 15. _Tympanuchus pallidicinctus_ 2L. Medial
    view of the muscles of the left leg. The following muscles have
    been removed: extensor iliotibialis lateralis, extensor
    iliotibialis anticus, ambiens, flexor cruris lateralis (in part),
    flexor cruris medialis (in part), gastrocnemius pars externa
    and pars interna, and peroneus longus. × 1.                         400

  FIG. 16. _Tympanuchus pallidicinctus_ 2L. Lateral
    view of the muscles of the left leg. The following muscles,
    in addition to those listed for Fig. 14, have been removed:
    ambiens, vastus lateralis pars lateralis, vastus medialis (except
    for part of patellar tendon), extensor iliofibularis, flexor
    cruris lateralis (in part), flexor perforans et perforatus
    digiti II, and flexor perforans et perforatus digiti III. × 1.      401

  FIG. 17. _Tympanuchus pallidicinctus_ 2L. Lateral
    view of the muscles of the left leg. The following muscles, in
    addition to those listed for Fig. 16, have been removed: vastus
    lateralis pars postica, gluteus profundus, flexor cruris medialis
    (in part), caudofemoralis, flexor perforatus digiti IV, and
    tibialis anticus. × 1.                                              402

  FIG. 18. _Tympanuchus pallidicinctus_ 2L. Lateral
    view of the muscles of the left leg. The following muscles, in
    addition to those listed for Fig. 17, have been removed: patellar
    tendon, iliacus, iliotrochantericus medius, flexor cruris
    lateralis, flexor cruris medialis, flexor ischiofemoralis,
    adductor superficialis, femorocruralis, gastrocnemius pars media,
    flexor perforatus digiti III, flexor perforatus digiti II, flexor
    hallucis longus, plantaris, flexor digitorum longus, popliteus,
    and extensor digitorum longus. × 1.                                 403

  FIG. 19. _Tympanuchus pallidicinctus_ 2L. A.
    Posterior view of the muscles of the left shank. The following
    shank muscles, in addition to those listed for Fig. 17, have
    been removed: gastrocnemius pars media, flexor perforatus
    digiti III, and flexor perforatus digiti II. × 1. B. Posterior
    view of the proximal end of the shank, showing the most deeply
    situated muscle. × 1. C. Lateral view of the head of the left
    femur and the middle part of the pelvis, showing the deepest
    part of M. obturator. × 1. D. Medial view of the posteroventral
    part of the left side of the pelvis, showing the intrapelvic part
    of M. obturator. × 1. E. Anterior view of the left
    tarsometatarsus, showing the dorsal intrinsic muscles of the
    foot. × 1-1/2. F. Posterior view of the left tarsometatarsus,
    showing the ventral intrinsic muscles of the foot. × 1-1/2.         404

  FIG. 20. A-D. Dorsal views of M. iliotrochantericus
    medius, showing its relationship to femoral notch. × 1. In D,
    note absence of femoral notch and location of branch of femoral
    nerve. A. _Tympanuchus pallidicinctus_ 2L. B. _T. cupido
    pinnatus_ 4L. C. _Pedioecetes phasianellus jamesi_ 1L.
    D. _T. pallidicinctus_ 3L.
    E. Medial view of distal end of M. flexor cruris medialis of
    _P. p. jamesi_ 4L. × 1. Part of insertion is covered by
    medial collateral ligament.
    F,G. Lateral views of posteroproximal corner of M. extensor
    iliotibialis lateralis (removed from specimen). × 1. F.
    _T. pallidicinctus_ 2L. G. _P. p. jamesi_ 3L.
    H,I. Dorsolateral views of M. piriformis. × 1. H. _P.
    p. jamesi_ 1L. I. _T. cupido attwateri_ 1L.
    J. Lateral view of M. caudofemoralis pars caudifemoralis
    (removed from specimen) of _T. c. pinnatus_ 4L. × 1.
    K. Lateral view of extrapelvic part of M. obturator of
    _T. pallidicinctus_ 3L (bones not shown). × 2.
    L,M. Region surrounding obturator foramen of _T.
    pallidicinctus_ 3L, showing points of attachment of three
    parts of M. obturator (muscles removed). × 3. L. Lateral
    view. M. Medial view.
    N. Anterior view of left tarsometatarsus of _P. p.
    jamesi_ 4L, showing dorsal intrinsic muscles of foot.
    × 1-1/2. Tendon of M. extensor digitorum longus has been
    removed.                                                            406




INTRODUCTION


The purposes of this study were: (1) to obtain information on individual
variation in the anatomy of the muscles and nerves of the leg of
_Tympanuchus cupido pinnatus_ (Greater Prairie Chicken), _T. c.
attwateri_ (Attwater's Prairie Chicken), _T. pallidicinctus_ (Lesser
Prairie Chicken), and _Pedioecetes phasianellus jamesi_ (Sharp-tailed
Grouse); (2) to determine whether or not the two species of the genus
_Tympanuchus_ differ constantly in the myology of the leg; and (3) to
determine what constant differences in the myology of the leg exist
between the two closely related genera _Tympanuchus_ and _Pedioecetes_.

These particular birds were chosen because they are closely related, and
closely resemble one another in habitats occupied and in patterns of
behavior. It was desired to study examples that showed as few adaptive
differences as possible among the grouse. Series of each of the three
species of grouse were readily obtainable, making it possible to draw
comparisons at the level of individuals, subspecies, species, and
genera.

The study here reported on was begun in the spring of 1957 and was
completed in the autumn of 1961.

Prior work on the muscles of the leg of birds has been reviewed by
Hudson (1937) and Hudson, _et al._ (1959). Only papers dealing with the
innervation of the leg in birds are reviewed below.

     DeMan (1873) treated the nerves of _Paradisea papuana_, _Corvus
     monedula_, and the chicken; he also commented briefly on a few
     other species. Jhering (Ihering, 1873) briefly described the
     lumbosacral plexus in approximately a dozen birds, but illustrated
     only two. Gadow (1880) described the nerves in _Struthio_, _Rhea_,
     and _Casuarius_; his paper contains some excellent illustrations of
     nerves. Unfortunately, the text is marred by numerous confusing
     typographical errors. Carlsson (1884) described the nerves of
     _Eudyptes chrysolopha_, _Alca torda_, _Mergulus alle_, and _Mormon
     arcticus_. Gadow (1891) described the nerves in a study that
     included a large variety of birds, but published few illustrations.
     DuToit (1913) described the lumbosacral plexus of the chicken.
     Romer (1927) gave the innervation of the hip and thigh muscles in
     the chicken, but did not cover the lumbosacral plexus. Appleton
     (1928) gave the innervation, in various birds, only of those
     muscles of the hip and thigh that are supplied by the tibial and
     peroneal nerves; he did not include the lumbosacral plexus.
     Sudilovskaya (1931) described the nerves of _Struthio_, _Rhea_, and
     _Dromaeus_ (_Dromiceius_). Unfortunately, his illustrations are
     almost useless as far as the nerves are concerned. Boas (1933)
     described the lumbosacral plexus in a large number of birds. His
     extensive account includes numerous good illustrations. Howell
     (1938) listed the innervation of the hip and thigh muscles in the
     chicken; he did not include the lumbosacral plexus. Fisher (1946)
     listed the innervation of the muscles of vultures, but did not
     include the lumbosacral plexus. Wilcox (1948) gave the innervation
     of the muscles of _Gavia immer_, but did not include the lumbosacral
     plexus. Fisher and Goodman (1955) described the nerves in the Whooping
     Crane. Papers by Chomiak (1950) and Yasuda, _et al._ (1959), both
     dealing with the chicken, were not examined.




MATERIALS AND METHODS


Complete dissections of the muscles and nerves were made in eight legs
(of five specimens) of the Lesser Prairie Chicken (_Tympanuchus
pallidicinctus_), six legs (of four specimens) of the Greater Prairie
Chicken (_T. cupido pinnatus_), three legs (of two specimens) of
Attwater's Prairie Chicken (_T. cupido attwateri_), and six legs (of
four specimens) of the Sharp-tailed Grouse (_Pedioecetes phasianellus
jamesi_).

For convenience and simplicity of reference, each specimen has been
designated by a symbol consisting of the first letter of the genus and
of the species (and also of the subspecies in _T. cupido_) plus a
number. The letter "L" or "R" is added to indicate the left or right
leg. Thus the symbol T.p. 1L refers to the left leg of specimen number
one of _T. pallidicinctus_.

All specimens are in the University of Kansas Museum of Natural History.
The catalogue number of each specimen, and the legs of it that were
dissected, are listed below.

    T.p. 1L,R          KU38520              T.c.p. 4L          KU38518
    T.p. 2L,R          KU38521              T.c.a. 1L,R        KU36617
    T.p. 3L,R          KU38522              T.c.a. 2L          KU36618
    T.p. 4L            KU38523              P.p. 1L,R          KU38526
    T.p. 5R            KU38524              P.p. 2L            KU38527
    T.c.p. 1L,R        KU38515              P.p. 3L,R          KU38528
    T.c.p. 2L,R        KU38516              P.p. 4L            KU38529
    T.c.p. 3L          KU38517

The specimens were injected in the field either with formalin (10%) or
embalming fluid, except for those of _T. c. attwateri_, which were
frozen; the latter were later injected with embalming fluid. Injection
in all the birds was by hypodermic syringe into all major muscle masses,
into the body cavities, and subcutaneously in the neck, wings, and feet.
In those specimens injected with embalming fluid, the body cavities were
injected with formalin. The embalming fluid consisted of 70 per cent
alcohol, glycerin (or propylene glycol), and formalin (full strength) in
the approximate ratio of 78:20:2, respectively. This fluid gave good
preservation; these specimens had the advantages of lacking almost
entirely the irritating odor of formalin and of having pliable tissues.
The skin of those specimens originally injected with formalin was slit
in several places and they were transferred to crocks containing
embalming fluid (without the formalin). After a period of many weeks,
with two changes of fluid, most of the formalin odor was eliminated and
the muscles were sufficiently pliable to be easily dissected. All
specimens were kept in containers filled with embalming fluid. No mold
ever appeared, even though no phenol or other chemical was added.

To facilitate comparison, two or three specimens were frequently
dissected simultaneously. The nerves and smaller muscles were dissected
with the aid of a stereoscopic microscope mounted on a long movable arm.
In order satisfactorily to expose the lumbosacral plexus the posterior
half of the sternum and pectoral muscles, as well as the abdominal
viscera, were removed.

To insure more nearly accurate proportions, drawings of the pelvis and
of some of the muscles were made with the aid of photographs of the
several specimens listed above.




TERMINOLOGY


_Skeleton_

The majority of the osteological terms used in the present paper are
those used by Howard (1929); however, many skeletal features are not
named by Howard. Since names for most of these parts were not found in
the other literature examined, it was necessary for me to propose terms
for them. Most of this new terminology pertains to the pelvis. All of
the osteological terms used in the present paper, whether used by Howard
or not, are briefly defined below. Those of the pelvis are illustrated
in fig. 1. Most of the remaining terms are illustrated by Howard (1929).


PELVIS

The _median dorsal ridge_ is the blunt ridge in the midline of the
anterior part of the synsacrum formed by the neural spines of the
vertebrae. The _antitrochanter_, on the posterodorsal rim of the
acetabulum, is a pyramid-shaped projection that articulates with the
proximal end of the femur. The _anterior iliac crest_ is a ridge along
the dorsomedial border of the ilium, beginning almost at the anterior
end of that bone; the crest curves laterally as it extends posteriorly
and (for purposes of the present definition) ends at the level of the
posterior edge of the antitrochanter, where the crest is continuous with
the lateral iliac process. The _lateral iliac process_ is a pronounced,
laterally or ventrolaterally, projecting ridge on the ventrolateral
surface of the ilium posterior to the level of the antitrochanter; the
process does not extend as far as the posterior end of the ilium. The
_lateral ischiatic ridge_ is a relatively slight ridge continuous with
the posterior end of the lateral iliac process and curves
posteroventrally across the lateral surface of the posterior part of the
ischium; the ridge extends to the ventral edge of the ischium in some
individuals and not in others. The _dorsolateral iliac ridge_ begins at
the lateral edge of the ilium near the posterior end of the lateral
iliac process and curves posteromedially and somewhat dorsally,
extending to the posterior edge of the ilium. The _lateral iliac fossa_
is the concavity below the overhanging lateral iliac process. The
_ilio-ischiatic fenestra_ is a large oblong opening behind the
acetabulum between the ilium and the ischium. The _obturator foramen_ is
a small oval opening posteroventral to the acetabulum between the
ischium and the pubis. The _ventral ischiatic tubercle_ is the angle
formed by the ventrally projecting ischium at the point (near its
midlength) where the ischium overlaps and lies lateral to (and fused to)
the pubis. The _pectineal process_ is an anterolaterally directed
projection of the ventrolateral edge of the ilium anteroventral to the
acetabulum. The _femoral notch_ of the ilium is a shallow notch in the
ventrolateral edge of the ilium approximately halfway between the last
rib and the pectineal process. The _oblique iliac crest_ is a pronounced
blunt ridge on the ventral surface of the ilium and extends from the
posterolateral corner of the last synsacro-thoraco-lumbar vertebra to
near the anteroventral border of the ilio-ischiatic fenestra. The
_internal ilio-ischiatic crest_ is more or less continuous with the
oblique iliac crest and extends posteriorly along the dorsal border of
the ischium (forming the ventral border of the ilio-ischiatic fenestra),
and then curves sharply dorsomedially onto the ventral surface of the
ilium. The _iliac recess_ is a concavity dorsolateral to the sharply
curving posterior end of the internal ilio-ischiatic crest.

[Illustration: FIG. 1. Pelvis of _Tympanuchus pallidicinctus_. A.
Lateral view. × 1. B. Ventral view. × 1-1/8.]

The terminology applied to the synsacral vertebrae by different authors
varies. The terminology proposed by DuToit (1913) is employed in the
present account. See my fig. 1B. This terminology differs considerably
from that used by Howard (1929). DuToit divides the fused synsacral
vertebrae into the following five groups, listed in anteroposterior
sequence: (1) _synsacro-thoracic_, which bear movable ribs; (2)
_synsacro-thoraco-lumbar_, which lack movable ribs but possess well
developed laterally directed parapophyses, in addition to the more
dorsally directed diapophyses; (3) _synsacro-lumbar_, which lack
parapophyses, although possessing inconspicuous diapophyses; these
vertebrae are shortened anteroposteriorly and are so firmly fused
together that often the number present can be determined only by
counting the intervertebral foramina; (4) _synsacro-sacral_, which have
much more pronounced transverse processes than do the synsacro-lumbar
vertebrae; these transverse processes are expanded distally where they
fuse with the ilium and represent both parapophyses and diapophyses
partly or completely fused together plus sacral ribs (detectable only in
the embryo); there are considered to be two of these vertebrae; they are
situated at approximately the level of the acetabulum; (5)
_synsacro-caudal_, which include the remainder of the fused vertebrae;
no marked gross morphological features differentiate the synsacro-sacral
and the synsacro-caudal groups of vertebrae. The boundaries between all
but the last two groups of vertebrae are usually, but not always, easily
determined. It may be difficult to determine whether a vertebra with
rudimentary parapophyses belongs to the synsacro-thoraco-lumbar or the
synsacro-lumbar group. Sometimes a parapophysis will be better developed
on one side of a vertebra than on the other.


FEMUR

The _trochanter_ is a large squarish tuberosity on the lateral surface
of the proximal end of the femur. The _trochanteric ridge_ is a sharp,
longitudinal (relative to the femur) ridge forming the anterior edge of
the trochanter. The _obturator ridge_ is a short, blunt, longitudinal
ridge forming the posterior edge of the trochanter. The _anterior
intermuscular line_ is a slight ridge extending distally from the
trochanteric ridge. The _posterolateral intermuscular line_ is a slight
ridge extending distally from the obturator ridge. The _posterior
intermuscular line_ is a slight, longitudinal ridge on the mid-posterior
surface of the femur. The _internal condyle_ is a large rounded
articular prominence on the medial side of the distal end of the femur.
On the lateral side of the distal end of the femur are two articular
prominences--the lateralmost, smaller one is the _fibular condyle_,
separated by the _fibular groove_ (visible from posterior aspect only)
from the larger and more medial _external condyle_. The _popliteal area_
is a depression on the posterior surface of the distal part of the femur
immediately proximal to the condyles.


TIBIOTARSUS AND FIBULA

The _inner cnemial crest_ is pronounced and directed anteriorly on the
anterior surface of the proximal end of the tibiotarsus. The _outer
cnemial crest_ is pronounced and directed anterolaterally on the
anterolateral surface of the proximal end of the tibiotarsus. The
_rotular crest_ is transverse and forms the anterior border of the
proximal end of the tibiotarsus; the crest extends between the dorsal
ends of the two cnemial crests and also extends medial to the inner
cnemial crest. The _fibular crest_ is longitudinal on the lateral
surface of the tibiotarsus and fuses with the middle part of the fibula.
The _fibular tubercle_ is small and on the lateral surface of the fibula
near the level of the middle of the fibular crest. The _anteromedial
intermuscular line_ is a slight ridge extending from the inner cnemial
crest down the anteromedial surface of the tibiotarsus. The
_anterolateral intermuscular line_ is a slight ridge extending from the
fibular crest down the anterolateral surface of the tibiotarsus. The
_supratendinal bridge_ is a transverse bony arch over a longitudinal
groove near the distal end of the anterior surface of the tibiotarsus.


TARSOMETATARSUS

The _hypotarsus_ is a large, pronounced, squarish protuberance on the
posterior surface of the proximal end of the tarsometatarsus and
contains grooves and canals for the passage of the flexor tendons. The
longitudinal ridges forming the lateral and medial edges of the
posterior surface of the hypotarsus are termed _calcaneal ridges_. The
_posterior metatarsal crest_ is long and sharp; it is continuous with
the medial calcaneal ridge that extends most of the way down the
posterior surface of the tarsometatarsus medial to the midline; there is
an opening between this crest and the tarsometatarsus immediately distal
to the hypotarsus. The _medial metatarsal depression_ is large; it is on
the medial surface of the proximal end of the tarsometatarsus. The
_anterior metatarsal groove_ is a longitudinal groove in the midline of
the proximal part of the anterior surface of the tarsometatarsus. The
three _trochleae_ are large rounded articular prominences at the distal
end of the tarsometatarsus; there is one at the base of each of the
digits II, III, and IV. The term _distal foramen_ (as used by Howard)
refers to a short, anteroposteriorly directed canal that perforates the
tarsometatarsus a short distance proximal to the intertrochlear notch
between the trochleae for digits III and IV. Beginning at the middle of
this canal and extending distally at a right angle to it is the
_intertrochlear canal_, which opens via the terminal foramen into the
intertrochlear notch between the trochleae for digits III and IV.


_Nerves_

For ease of description I have coined terms for the major divisions of
the femoral and sciatic nerves.


_Muscles_

My terminology follows that of Fisher (1946) and Fisher and Goodman
(1955) except for Mm. femoritibialis externus, flexor cruris lateralis
(accessory head), and obturator internus et externus. Fisher (1946:547)
states that most of his names for the hip and thigh muscles are those of
Howell (1938) and the names for the shank and foot muscles are those of
Hudson (1937). Fisher deviates, without explanation, from Howell's
terminology in respect to Mm. vastus medialis and femoritibialis
internus, M. caudofemoralis, M. flexor cruris lateralis, and Mm.
obturator internus and obturator externus. Fisher's synonymy of these
muscles (1946: table 42) is in error. Fisher understandably deviates
from Hudson in respect to Mm. extensor brevis digiti III and extensor
proprius digiti III (see Holmes, 1962), although Fisher's synonymy is in
error here. See my table 1.

     I am not using Fisher and Goodman's term femoritibialis externus;
     this muscle is here considered as a part of M. vastus lateralis. A
     great deal of confusion surrounds the terminology of the muscle
     complex here termed Mm. vastus lateralis and vastus medialis.
     Hudson (1937), Hudson, _et al._ (1959), Fisher (1946), and Fisher
     and Goodman (1955) have used different terminology for this
     complex. Most of the confusion stems from Gadow's (1891) unclear
     description of this complex, which he subdivided into two units
     termed Mm. femori-tibialis externus and femori-tibialis medius.
     Many birds have three parts to this complex. It is difficult to
     determine how to apply Gadow's two terms to these three parts. As
     nearly as I can determine, the correct method is that of Hudson,
     _et al._ (1959); but because Gadow's terms have been used in
     different ways (even by the same worker), it seems best to abandon
     these terms. Berger (1956:272) believes that the muscle unit that
     Fisher and Goodman term M. femoritibialis externus represents a
     head of M. vastus lateralis; I am accepting his opinion. For the
     three parts of the complex under discussion, I am using the terms
     M. vastus medialis and M. vastus lateralis pars lateralis and pars
     postica.

     Fisher (Fisher, 1946; Fisher and Goodman, 1955) considers the
     muscle here termed M. femorocruralis as an accessory head of M.
     flexor cruris lateralis. The two muscle units in question are
     closely associated; they insert broadly on opposite sides of a
     common tendinous raphe. Howell (1938:73) considers this to be a
     secondary fusion of unrelated muscles. Romer (1927:366) states that
     in the chick embryo M. femorocruralis is in reality a shank muscle
     that migrates into the thigh during development. Therefore,
     Fisher's usage of a single name for these two unrelated muscles is
     unsatisfactory. I am using Howell's terminology in which the name
     flexor cruris lateralis represents the main head only of Fisher's
     M. flexor cruris lateralis and the name femorocruralis represents
     Fisher's accessory head.

     Gadow (1891) divides the obturator complex into two muscles (or
     muscle groups), which he terms M. obturator and Mm. accessorii M.
     obturatoris. He states that the former is homologous with the
     mammalian obturator internus and the latter with the obturator
     externus. Hudson (1937), accepting Gadow's homologies, renamed
     these muscles M. obturator internus and M. obturator externus.
     Nearly all subsequent workers have followed Hudson's terminology,
     with its implication that these muscles are homologous with the
     mammalian muscles of the same name. Howell (1938) is an exception.
     He points out (pp. 78, 79) that the obturator internus of Hudson is
     homologous with the obturator externus of mammals. His evidence is
     convincing: "In origin the obturator is somewhat suggestive of the
     mammalian obturator internus, for which it has uniformly been
     mistaken. That the latter interpretation is incorrect, however, is
     attested by the facts that it receives twigs of n. obturatorius
     within the pelvis, passes _through_ the obturator foramen rather
     than dorsal to the border of the ischium, and it is segregated from
     any muscle with tibial innervation. Insertion has shifted only to a
     slight and unimportant degree as compared with that of the
     mammalian obturator externus, and beyond question it is the
     equivalent of that muscle. The stimulus for a longer muscle, has
     been the same, resulting in the extension of origin to within the
     pelvis of the externus in birds and the internus in mammals, but
     the obturator internus is an extension of a part of the gemellus
     mass and this does not occur in any vertebrate class but Mammalia."
     Howell applies the term M. obturator to the entire obturator
     complex.

Romer (1927), studying the development of the thigh musculature in chick
embryos, concluded that the entire obturator complex is homologous with
the mammalian obturator externus plus quadratus femoris. He considered
the avian M. flexor ischiofemoralis to be the homologue of the mammalian
obturator internus.

Gadow, in his work on the ratites (1880:34), states that M. obturator
(obturator internus of Hudson) cannot be homologous to the mammalian
obturator internus, but must represent the obturator externus. His
reasoning is as follows: "Als M. pectineus kann man diesen Muskel nicht
auffassen, da er auf der Aussenfläche des Trochanter major inserirt,
ferner auch nicht als M. obturator internus der menschlichen Anatomie,
da er nicht vom Plexus ischiadicus, sondern vom Plexus cruralis aus
innervirt wird. Seiner Innervation und Insertion nach wäre er nur mit
dem M. obturator externus zu vergleichen, wobei er seinen Ursprung im
Verhältniss zum Menschen nur bedeutend weiter auf das Os ischii und Os
pubis distalwärts ausgedehnt hätte und so allerdings der Lage nach mit
Ausnahme seines Insertionsdrittels ein 'internus' geworden wäre."

Since Gadow gives different homologues for M. obturator in two of his
works (1880 and 1891), one would suspect that he had changed his opinion
in the interim; however, there is no evidence that he did so. In 1880 he
gives supporting evidence (quoted above) for his view; in 1891 he does
not. After describing (1891:173) how the origin of M. obturator in bird
ancestors presumably migrated from a location outside the pelvis to a
position inside the pelvis prior to the meeting of the pubis and ischium
external to the muscle, he states: "Eine ähnliche Entwicklung ist für
den _Obturator internus_ der Säugethiere anzunehmen, welchem der _M.
obturator_ der Vögel entspricht." A similar development in mammals is
impossible, owing to the different relationship of the muscle to the
pelvic bones in this class. Gadow says nothing more about the mammalian
homologue of M. obturator. In view of this discrepancy, Gadow can hardly
be considered as a supporter of the idea that the avian M. obturator is
homologous with the mammalian obturator internus.

The evidence is conclusive, it seems to me, that the obturator internus
of Hudson is not homologous with the mammalian obturator internus.
Therefore, the term obturator internus is inappropriate for the avian
muscle and must be abandoned. I shall follow Howell (1938) in naming the
entire obturator complex M. obturator. This term, of course, is not used
in the sense in which it is used by Gadow. The use of the term obturator
externus for the entire complex is avoided because it may not correspond
exactly to the mammalian obturator externus. As mentioned previously,
Romer considers the avian muscle to be homologous not only with the
mammalian obturator externus but also with the quadratus femoris.

I am following the policy of Wilcox (1948) and Berger (1952) in
latinizing the term anterior, changing it to anticus. When preceded by
the feminine word pars, the feminine ending is used (antica).

In table 1 my terminology is compared with that of Fisher and Goodman
(1955), Howell (1938), Hudson (1937), and Gadow (1891). The terminology
of Fisher (1946) is identical with that of Fisher and Goodman (1955)
except that in his earlier work Fisher did not describe or name M.
femoritibialis externus, and M. lumbricales of his earlier work is not
mentioned in his later work. The terminology of Hudson, _et al._ (1959)
is identical with that of Hudson (1937) except that the manner in which
the femoritibialis complex is subdivided is identical with that of Gadow
(1891) and different from that in Hudson's earlier work; also the
abbreviations p. ext. and p. int. are substituted in his later paper for
pars anterior and pars posterior, respectively, of M. adductor longus et
brevis.




ACKNOWLEDGMENTS


I gratefully acknowledge the generous help of Professor A. Byron
Leonard, under whose guidance this study was conducted and thank
Professor E. Raymond Hall, Professor Howard A. Matzke, and Dr. Irwin
Baird for numerous helpful suggestions and criticisms.

For help in collecting specimens I thank J. R. Alcorn, W. C. Glazener
(through the courtesy of the Texas Game and Fish Commission), Dr.
Harrison B. Tordoff, Jerry Tash, William Brecheisen, and Louis
Brecheisen. I thank also Edwin Gebhard of the Kansas Forestry, Fish and
Game Commission for help in locating the Lesser Prairie Chickens.

I am grateful for the assistance of Mrs. Chester Alexander and Dr. L. C.
Dahl in translating a Russian and a Dutch reference, and thank George
Young and James Bee for making equipment used in my study.

All of the original drawings except fig. 1 were made by me, although the
final inking of figs. 12 through 19 was done by Bret Waller. Fig. 1 was
drawn by Kay Swearingen.

I was aided in this study during the summer of 1960 by a research grant
from the University of Kansas.




SKELETON


Although no special study was made of the skeleton, certain conspicuous
variations are discussed here.

There are a few pronounced differences between the pelvis of
_Tympanuchus_ and that of _Pedioecetes_. Whereas in the former the thick
lateral iliac process has a pronounced overhang with the ventral edge
lateral to the ischium (fig. 1), in _Pedioecetes_ there is no overhang
at all and the edge of this process is much thinner. The ischium in
_Pedioecetes_ is wider (in dorsoventral extent), especially posteriorly,
than in _Tympanuchus_. In _Tympanuchus_ the posteroventral margin of the
ischium is rounded and is free from the pubis, whereas in _Pedioecetes_
it is pointed and fused with the pubis.

In _Tympanuchus cupido_ (both subspecies) the lateral iliac process
extends farther ventrally than in _T. pallidicinctus_, approaching or
extending ventral to the level of the pubis in the former species; also
the edge of this process is thicker in _T. cupido_.

All specimens studied have a single synsacro-thoracic vertebra. The
number of combined synsacro-thoraco-lumbar and synsacro-lumbar vertebrae
is eight in each specimen of _Tympanuchus_ and in one specimen of
_Pedioecetes phasianellus jamesi_ and is seven in three specimens of the
latter. In most specimens of _Tympanuchus_ there are three
synsacro-thoraco-lumbar and five synsacro-lumbar vertebrae, although in
two specimens (_T. pallidicinctus_) there are four of each group; in one
of these latter two specimens the parapophysis on one side of the fourth
synsacro-thoraco-lumbar vertebra is small. The first (of five)
synsacro-lumbar vertebra has a rudimentary parapophysis on one side in
one specimen of _Tympanuchus_ and on both sides in another specimen. One
specimen of _Pedioecetes phasianellus jamesi_ has five synsacro-lumbar
vertebrae and the others have four; all have three
synsacro-thoraco-lumbar vertebrae.




NERVES


For each nerve (or plexus) the condition found in most specimens of the
Lesser Prairie Chicken (_T. pallidicinctus_) is described first.
Following this, variations from the typical _T. pallidicinctus_
condition are given for _T. pallidicinctus_, then for _T. cupido_ (both
subspecies considered together), and finally for _P. p. jamesi_.


=_Lumbosacral Plexus_=, Figs. 2, 3

_T. pallidicinctus_

DESCRIPTION.--Eight spinal nerves contribute to the lumbosacral plexus.
These are the second through the ninth synsacral spinal nerves (S2 to
S9). The entire ventral ramus of each of these nerves, excepting S2 and
S9, contributes to this plexus. The ventral ramus of S2 divides into two
branches, only the posterior of which contributes to the plexus; the
anterior branch directly innervates muscles of the abdominal wall (as
does the entire ventral ramus of S1). The ventral ramus of S9 divides
into two branches, only the anterior of which contributes to this
plexus; the posterior branch contributes to the more posteriorly
situated pudendal plexus.

Each root of the plexus corresponds to a single spinal nerve except one
spinal nerve (S5--the furcal) that contributes a root to both the
femoral nerve and the sciatic nerve; thus typically the plexus has nine
roots (but see below). The four anteriormost roots (S2 to S5) contribute
to the femoral nerve, although the contribution from S2 is small. S3 and
S4 contribute to the obturator nerve. The five posteriormost roots (S5
to S9) contribute to the sciatic nerve, although the contribution from
S9 is relatively small.

INDIVIDUAL VARIATION.--In all specimens (of all species) examined, the
right and left sides of the plexus in any one individual were
practically identical. In T.p. 2 (fig. 2B), there appear to be two
furcal nerves; S5 is typical, but a small branch of S4 apparently also
contributes to the sciatic nerve. In T.p. 5, S9 is unique in dividing
into three branches; the anterior two join the sciatic nerve separately;
the posterior one joins the pudendal plexus as usual.

_T. cupido_

INDIVIDUAL VARIATION.--S2 or S5, or both, may contribute to a limited
extent to the obturator nerve. In T.c.p. 3 (fig. 3A) and T.c.a. 1 and 2,
much of the plexus has shifted one segment anteriorly, relative to the
synsacral vertebrae (the so-called prefixed condition); the roots of the
femoral nerve are S2, S3, and S4 (all large); the furcal nerve is S4 (in
T.c.a. 1, S5 gives an extremely small root to the femoral nerve, thus
making two furcal nerves); six roots (S4 to S9) contribute to the
sciatic nerve; S3 and S4 remain as the main contributors to the
obturator nerve except in T.c.a. 2 in which only S2 and S3 contribute to
it.

_P. p. jamesi_

INDIVIDUAL VARIATION.--In P.p. 1, the plexus resembles the typical
condition in _T. pallidicinctus_. In P.p. 2, 3, and 4, the plexus is
prefixed. P.p. 2 resembles T.c.p. 3. In P.p. 3 and 4 (fig. 3B) there are
two furcal nerves (S4 and S5); S2 to S4 are the main contributors to the
femoral nerve; only S2 and S3 contribute to the obturator nerve; S4 to
S9 contribute to the sciatic nerve (the anteriormost and posteriormost
roots are small).


=_Femoral Nerve_=, Figs. 4, 5

_T. pallidicinctus_

DESCRIPTION.--The femoral nerve is short, dividing inside the pelvis
into six major divisions--anterior, middle, posterior, anterodorsal,
dorsal, and posterodorsal. The anterodorsal and posterodorsal divisions
are short, failing to extend so far laterally as the inguinal ligament;
the posterodorsal division is also small and is usually covered by other
divisions and is not visible when viewed from the ventral side.

The anterior division passes ventral to Mm. iliotrochantericus medius
and iliacus and dorsal to the anterior end of the inguinal ligament. The
division branches into two parts. The anterior part extends around the
posterior border of M. extensor iliotibialis anticus and sends several
twigs to the lateral surface of this muscle. The posterior part passes
between the proximal parts of Mm. extensor iliotibialis anticus and
extensor iliotibialis lateralis and supplies the skin.

The middle division passes ventral to Mm. iliotrochantericus medius and
iliacus and dorsal to the inguinal ligament. The division branches into
a large but variable number of parts. A variable number of branches
(usually two) pass posterior to M. extensor iliotibialis anticus and
penetrate the medial surface of M. extensor iliotibialis lateralis.
Several branches supply the fused Mm. vastus lateralis and vastus
medialis. The posteriormost branch of this division passes between Mm.
ambiens and vastus medialis, giving twigs to the lateral surface of M.
ambiens, and sometimes also to the medial surface of M. vastus medialis,
and terminates in M. femoritibialis internus.

The posterior division, which does not subdivide, spirals completely
around M. psoas (passing in turn anterior, dorsal, posterior, and
ventral to it) and gives twigs into this muscle. This nerve then extends
distally into the proximal part of the shank and there has a nonmuscular
termination.

The short, thick anterodorsal division, partly covered by the anterior
division, turns dorsally and passes through the femoral notch of the
ilium and penetrates the deep surface of M. gluteus profundus.

The slender dorsal division passes ventral to M. iliotrochantericus
medius and dorsal to the inguinal ligament and penetrates the ventral
surface of M. iliacus.

The small, short posterodorsal division penetrates the ventral surface
of M. iliotrochantericus medius.

INDIVIDUAL VARIATION.--In two legs the anterior division gives a twig or
two twigs to M. extensor iliotibialis lateralis. The dorsal division may
fuse proximally with either the anterior or middle division, thus
appearing to be a branch of one of these divisions. In one leg (fig.
5A), there are two separate branches (both fused with the middle
division) to M. iliacus. On both sides of one specimen (fig. 5A), the
anteriormost branch of the middle division, which supplies M. extensor
iliotibialis lateralis, gives off a twig that anastomoses with the
branch of the anterior division that supplies M. extensor iliotibialis
anticus. On both sides of another specimen, the anterodorsal division
passes lateral to the anterior end of M. iliotrochantericus medius
instead of through the femoral notch, which is lacking.

_T. cupido_

INDIVIDUAL VARIATION.--In three legs, the anterior division gives twigs
into M. extensor iliotibialis lateralis. The dorsal division is fused
proximally with the middle division in one instance. In three cases, a
twig from the middle division anastomoses with the branch of the
anterior division supplying M. extensor iliotibialis anticus. In the
example shown in fig. 5B, a twig comes off the cutaneous branch of the
anterior division, perforates the ventral part of M. iliacus, and
rejoins the cutaneous branch. In both legs of one specimen, the
cutaneous branch of the anterior division perforates the anterior edge
of M. extensor iliotibialis lateralis instead of passing between the
latter and M. extensor iliotibialis anticus. The posteriormost branch of
the middle division, which terminates in M. femoritibialis internus,
perforates the medial part of M. vastus medialis in one leg. In another
leg, one of the branches to the fused Mm. vastus lateralis and vastus
medialis sends a twig into M. extensor iliotibialis lateralis.

_P. p. jamesi_

INDIVIDUAL VARIATION.--In three legs, the anterior branch of the
anterior division is cutaneous and the posterior branch supplies M.
extensor iliotibialis anticus. The dorsal division may fuse proximally
with either the anterior or middle division. In one leg (fig. 4B), there
are two branches to M. iliacus, one associated with the anterior
division and one with the middle division.


=_Obturator Nerve_=

_T. pallidicinctus_

DESCRIPTION.--The long slender obturator nerve passes along the oblique
iliac crest and divides into several branches immediately before
reaching the obturator foramen. One or two branches, which do not pass
through the foramen, penetrate the superficial surface of M. obturator
pars postica. Several small branches (variable in number and
arrangement) pass through the obturator foramen and supply pars
ventralis, pars dorsalis, and pars antica of M. obturator. When pars
ventralis and pars dorsalis are fused, one branch perforates the
proximal end of this mass and reaches pars antica. One large branch
passes through the obturator foramen dorsal to the tendon of M.
obturator pars postica, then turns ventrally, passing lateral to the
latter; the branch passes between Mm. adductor superficialis and
adductor profundus and gives twigs to each of these two muscles.

INDIVIDUAL VARIATION.--None of significance in any of the three species.


=_Sciatic Nerve_=, Figs. 6, 7, 8, 9

_T. pallidicinctus_

DESCRIPTION.--The sciatic nerve passes through the anterior part of the
ilio-ischiatic fenestra. Several branches diverge from the nerve
immediately after it emerges from the fenestra. The main trunk of the
nerve then extends distally through the thigh deep to M. extensor
iliofibularis and superficial (lateral) to Mm. flexor ischiofemoralis,
caudofemoralis, adductor superficialis, and femorocruralis. The main
trunk subdivides into two large nerves--peroneal and tibial--that are
adjacent and bound to each other throughout the thigh; the peroneal
nerve lies anterior to the tibial. At the distal end of the thigh the
main trunk splits grossly into two large branches that diverge and enter
the shank. This division does not represent the separation between
peroneal and tibial nerves, as is sometimes assumed; the anterior branch
includes a part of the tibial nerve as well as the entire peroneal
nerve.

A longitudinal groove is visible grossly on the lateral surface of the
main trunk, except at the proximal end; distally a second groove is
visible posterior to the first one (fig. 6). The long anterior groove
indicates the boundary between the peroneal and tibial nerves; this
groove may disappear distally, although the posterior groove is always
visible distally. The posterior groove, which is continuous with the
division of the sciatic nerve into anterior and posterior branches,
represents the boundary between two divisions of the tibial nerve. (This
is discussed in detail below.) In the middle of the thigh the peroneal
and tibial nerves are enclosed in separate connective tissue sheaths,
although the two sheaths are fused together; the point of fusion is
marked by the anterior groove. If the two sheaths are slit open, the two
nerves can be removed and can be seen to be entirely separate. In the
proximal part of the main trunk the peroneal and tibial components are
enclosed in a single sheath and appear as an undivided trunk; but if the
sheath is removed, the two components can be pulled apart rather easily,
although there may be some intermingling of a few fibers. This
separation can be extended to a point proximal to the origin of all the
branches of the sciatic nerve; thus it can be determined which branches
arise from the peroneal component and which from the tibial. (These
branches arise from the sciatic nerve as, or immediately before, the
nerve passes through the ilio-ischiatic fenestra; since this level of
the intact nerve could not be adequately observed, it was necessary to
cut the nerve inside the pelvis and pull the intrapelvic part of the
nerve out through the ilio-ischiatic fenestra. In doing this, care had
to be taken to avoid damaging the most proximal branches.)

Three main branches arise from the peroneal component (apart from the
main trunk) and two from the tibial. Including the peroneal and tibial
components of the main trunk, the sciatic nerve can be divided into
seven major divisions--anterior peroneal, middle peroneal, dorsal
peroneal, posterior or main peroneal (contributes to main trunk),
anterior or main tibial (contributes to main trunk), middle tibial, and
posterior tibial. Farther distally, the posterior peroneal division
becomes the peroneal nerve and the anterior tibial division becomes the
tibial nerve. For descriptive purposes, the term peroneal (or tibial)
_nerve_ will be applied only where the nerve is enclosed in its own
sheath, but regardless of whether or not the sheath is fused with
another; proximal to this, where the separation may not be precise, the
terms peroneal (or tibial) _division_ or _component_ will be used.

The small anterior peroneal division arises from the anterior edge of
the sciatic nerve. Immediately after emerging from the ilio-ischiatic
fenestra, the division turns anteriorly and passes deep to M.
piriformis, to which the division gives a twig (in some cases more than
one twig), then continues forward to supply the posterior part of M.
gluteus profundus.

The middle peroneal division branches into two parts. One part
penetrates the deep surface of the anteroproximal part of M. extensor
iliofibularis. The other part emerges between the proximal ends of Mm.
extensor iliofibularis and vastus lateralis and penetrates the deep
surface of M. extensor iliotibialis lateralis.

The dorsal peroneal division arises from the posterodorsal part of the
peroneal component, then angles posteriorly, crossing the dorsal surface
of the anterior tibial division and superficially appears to arise from
the tibial component. The dorsal peroneal division usually subdivides
into two unequal branches, both of which penetrate the deep surface of
the proximal end of M. extensor iliofibularis.

The large middle tibial division soon subdivides into two branches that
pass posterodistally lateral to M. flexor ischiofemoralis. One branch
(usually the anterior one) passes lateral to M. caudofemoralis (both
heads) and emerges between Mm. extensor iliofibularis and flexor cruris
lateralis and enters the skin. The other branch passes deep to M.
caudofemoralis pars iliofemoralis, and divides into several branches.
Several tiny branches penetrate the deep surface of M. caudofemoralis
pars iliofemoralis. Another branch also enters the substance of the
latter and emerges from the ventral edge of it, giving a twig to pars
caudifemoralis, then passes lateral to pars caudifemoralis and enters M.
flexor cruris lateralis. Still another branch passes deep to both heads
of M. caudofemoralis and enters the anterior part of M. flexor cruris
medialis.

The small posterior tibial division arises from the posterior edge of
the sciatic nerve. The division diverges from the remainder of the
nerve, as the latter passes through the ilio-ischiatic fenestra, and
penetrates the dorsal surface of M. flexor ischiofemoralis.

Below the middle of the main trunk a bundle of fibers of moderate size
separates from the anterior edge of the tibial nerve, leaves the tibial
sheath, and enters its own sheath, lying superficially between the
tibial and peroneal sheaths (fig. 6). At the distal end of the thigh the
sheath enclosing this bundle of fibers remains fused with the posterior
edge of the peroneal nerve and passes with the latter (diverging from
the remainder of the tibial nerve) through the tendinous guide loop for
M. extensor iliofibularis, and then diverges from the peroneal nerve.
Since this bundle of fibers is distributed with the peroneal nerve, and
since the origin of the bundle may be easily overlooked, it has
sometimes been misinterpreted as a branch of the peroneal nerve, whereas
it almost certainly is a branch of the tibial nerve; this bundle will
here be termed the paraperoneal branch of the tibial nerve.

A small but long branch separates from the posterior edge of the
proximal end of the tibial nerve or from the tibial component proximal
to this and extends distally for some distance adjacent to the tibial
nerve, then passes posterodistally between Mm. extensor iliofibularis
and flexor cruris lateralis and supplies the skin.

A small branch separates from the anterior edge of the peroneal nerve a
short distance above the distal end of the main trunk and passes
distolaterally between Mm. extensor iliotibialis lateralis and extensor
iliofibularis and supplies the skin.

A twig comes off the medial surface of the tibial nerve near the distal
end of the main trunk, passes anteriorly deep to the peroneal nerve, and
penetrates the lateral surface of M. femorocruralis; in some cases two
twigs enter this muscle.

INDIVIDUAL VARIATION.--In one leg (fig. 7), the twig to M.
caudofemoralis pars caudifemoralis arises more proximally than usual and
perforates pars iliofemoralis independently of the branch to M. flexor
cruris lateralis. The nerve supplying M. flexor cruris lateralis does
not perforate M. caudofemoralis pars iliofemoralis, but passes deep to
it in three legs. In half the legs, the paraperoneal branch of the
tibial nerve, after extending a short distance in its own sheath, enters
the sheath of the peroneal nerve and appears grossly to unite with it;
if, however, the sheath is slit open, the paraperoneal branch can be
easily pulled apart from the posterior edge of the peroneal nerve; the
paraperoneal branch is again enclosed in its own sheath at the distal
end of the thigh. In one leg, the cutaneous branch of the peroneal nerve
perforates the posteroproximal part of M. gastrocnemius pars externa; in
three others, this branch is absent. In one of these last three legs
(fig. 7), the distal cutaneous branch of the tibial nerve is also
absent. In three legs (of different specimens), a minute twig from the
middle tibial division passes posteriorly deep to M. caudofemoralis pars
caudifemoralis toward the tail (fig. 7); this twig joins the pudendal
plexus in one leg; in the other two the twig could not be traced to its
termination. Minute twigs come off the peroneal nerve near the middle of
the thigh and enter M. extensor iliofibularis in some legs. In a few
cases, a minute nonmuscular twig arises from the peroneal nerve near the
distal end of the main trunk and passes anteriorly deep to M. vastus
lateralis pars postica (fig. 7).

_T. cupido_

INDIVIDUAL VARIATION.--In several legs, the nerve supplying M. flexor
cruris lateralis does not perforate M. caudofemoralis pars
iliofemoralis, but passes deep to it. The branch to M. flexor cruris
medialis arises from the posterior (rather than the middle) tibial
division in one instance (fig. 8). In one leg, a minute twig from the
middle tibial division passes posteriorly and joins the pudendal plexus;
in another, a similar twig is present but could not be traced to its
termination. In some specimens, minute twigs come off the peroneal nerve
near the middle of the thigh and enter M. extensor iliofibularis. In one
leg, a nonmuscular twig arises from the base of the cutaneous branch of
the peroneal nerve and passes anteriorly deep to M. vastus lateralis
pars postica. In another leg (fig. 8), a tiny additional twig arises
from the posterior edge of the tibial nerve and subdivides, one branch
joining the cutaneous branch of the middle tibial division and the other
joining the distal cutaneous branch of the tibial nerve.

_P. p. jamesi_

INDIVIDUAL VARIATION.--In both legs of one specimen, the branch to M.
flexor cruris medialis arises from the posterior (rather than the
middle) tibial division; in three legs, this branch arises as an
independent division of the tibial nerve (fig. 6). (Only in one leg does
this branch arise as in _T. pallidicinctus_.) The branch to M. flexor
cruris medialis perforates the lateral part of M. flexor ischiofemoralis
in one instance. In all legs except one (nerve possibly destroyed), a
second twig to M. flexor ischiofemoralis arises from the branch to M.
flexor cruris medialis (fig. 6). In one leg (fig. 9), an additional
branch, arising as an independent division of the sciatic nerve, enters
M. extensor iliofibularis distal to the point of entrance of the dorsal
peroneal division; this extra branch arises posterior (adjacent) to the
dorsal peroneal division, but it could not be determined with certainty
whether it arises from the peroneal or tibial component. A minute twig
from the branch to M. flexor cruris medialis passes posteriorly and
joins the pudendal plexus in one leg (fig. 6); in another, a similar
twig is present but could not be traced to its termination. In nearly
all the legs, minute twigs come off the peroneal nerve near the middle
of the thigh and enter M. extensor iliofibularis (fig. 6). In both legs
of one specimen, the paraperoneal branch enters the peroneal sheath
(although separable from the peroneal nerve). The distal branch to M.
femorocruralis gives off a long twig to M. gastrocnemius pars media in
one instance (fig. 6).


=_Peroneal Nerve_=, Fig. 10

_T. pallidicinctus_

DESCRIPTION.--The branch that is given off in the thigh has been
discussed above. The peroneal nerve passes, with the paraperoneal branch
of the tibial nerve, through the guide loop for M. extensor
iliofibularis. The peroneal nerve diverges from the paraperoneal branch
and passes along the anterior (proximal) edge of the tendon of M.
extensor iliofibularis medial to the common tendon of the lateral heads
of Mm. flexor perforatus digiti IV and flexor perforatus digiti II and
lateral to the common tendon of the anterolateral heads of Mm. flexor
perforatus digiti IV, flexor perforatus digiti II, and flexor perforatus
digiti III.

The peroneal nerve soon gives off a spray of branches that supplies the
following: femoral head of M. tibialis anticus, tibial head of M.
tibialis anticus (branch passes deep to femoral head), M. extensor
digitorum longus (branch passes deep to tibial head of M. tibialis
anticus), and M. peroneus longus. A part of the nerve may or may not
pass through a notch in the proximal end of the lateral head of M.
flexor digitorum longus. The nerve then extends distally along the
anterolateral edge of the latter muscle and subdivides into two long
branches. Gadow (1891) termed these branches the superficial peroneal
and the deep peroneal; his terminology will be used here.

The superficial peroneal branch, after giving off, near its proximal
end, one or two twigs into M. peroneus brevis, passes lateral to the
retinaculum for the tendon of M. tibialis anticus, then across the
intratarsal joint lateral to the latter, then lateral to the insertion
of M. tibialis anticus, where the branch subdivides. One of the two
resulting branches gives one or two twigs into M. extensor brevis digiti
IV, then terminates nonmuscularly in the digits. The other branch passes
between the main and accessory insertions of M. tibialis anticus and
joins the branch of the deep peroneal which supplies M. abductor digiti
II. (See next paragraph.)

The deep peroneal branch passes through the retinaculum for the tendon
of M. tibialis anticus, lying lateral, then deep, then medial to the
latter; it crosses the intratarsal joint medial to the latter.
Immediately above the insertion of M. tibialis anticus, the deep
peroneal branch divides, one branch passing on each side of the main
insertion. The branch passing lateral to the main insertion passes
between the latter and the accessory insertion (medial to the latter)
and is joined by a branch of the superficial peroneal nerve. This fused
branch extends distally between Mm. extensor hallucis longus and
extensor brevis digiti IV and medial to M. extensor brevis digiti III,
giving twigs into the latter and into M. abductor digiti II before
terminating nonmuscularly in the digits. The branch of the deep peroneal
nerve that passes medial to the main insertion of M. tibialis anticus
gives one or two twigs into the proximal head of M. extensor hallucis
longus, then terminates nonmuscularly in the digits.

INDIVIDUAL VARIATION.--In four legs, the branch of the superficial
peroneal nerve that usually joins the lateral branch of the deep
peroneal nerve is lacking (fig. 10B). In these legs it can be seen that
Mm. extensor brevis digiti III and abductor digiti II are supplied by
the deep peroneal nerve.

_T. cupido_

INDIVIDUAL VARIATION.--In two legs, the same branch that gives twigs
into the proximal head of M. extensor hallucis longus also sends a twig
into the distal head of this muscle (fig. 10C).

_P. p. jamesi_

INDIVIDUAL VARIATION.--None of significance.


=_Tibial Nerve_=, Fig. 11

_T. pallidicinctus_

DESCRIPTION.--The branches given off in the thigh have been discussed in
the account of the sciatic nerve. At the distal end of the thigh the
peroneal nerve and the paraperoneal branch of the tibial nerve diverge
from the remainder of the tibial nerve and pass through the tendinous
guide loop for M. extensor iliofibularis whereas the remainder of the
tibial nerve does not. This main part of the tibial nerve immediately
divides into three main divisions--lateral, posterior, and medial.

The lateral division passes between Mm. flexor perforatus digiti IV and
gastrocnemius pars externa and subdivides into two branches, one of
which penetrates the medial surface of M. gastrocnemius pars externa.
The other branch passes deep to the latter and sends twigs into the
posterior head of M. flexor perforans et perforatus digiti II, then
passes deep to the latter and enters M. flexor perforans et perforatus
digiti III.

The posterior division sends a branch into the medial head of M. flexor
perforatus digiti IV, then passes between the latter and the medial head
of M. flexor perforatus digiti III, and extends distally giving off
twigs to each of the three heads of M. flexor perforatus digiti IV, to
each of the two heads of M. flexor perforatus digiti III, and to each of
the three heads of M. flexor perforatus digiti II. The number and
arrangement of these twigs is variable.

The medial division passes medial to the medial head of M. flexor
perforatus digiti III, sends a twig to the lateral surface of M.
gastrocnemius pars media, then passes into the shank musculature between
Mm. plantaris and flexor hallucis longus, and sends a branch along the
medial edge of M. flexor hallucis longus that gives several twigs into
this muscle before terminating nonmuscularly. A small branch extends to
M. popliteus, another to M. plantaris, and another to the posterior head
of M. flexor digitorum longus. A nonmuscular branch passes between the
medial and posterior heads of M. flexor digitorum longus and extends
distally deep to this muscle. A long branch gives off near its proximal
end a variable number of twigs that pass deep to M. plantaris and enter
M. gastrocnemius pars interna; the branch then extends distally along
the lateral edge of M. plantaris and terminates nonmuscularly.

The paraperoneal branch diverges from the peroneal nerve, passing medial
and then distal to the insertion of M. extensor iliofibularis, whereas
the peroneal nerve passes proximal and then lateral to this insertion.
The paraperoneal branch passes deep to the lateral heads of Mm. flexor
perforatus digiti IV and flexor perforatus digiti II and superficial to
the tendon of the anterolateral head of M. flexor perforatus digiti IV
and then passes distally along the anterolateral borders of the latter
and the lateral head of M. flexor perforatus digiti III and the
posterolateral border of M. flexor digitorum longus. This branch is thus
separated from the peroneal nerve by M. flexor digitorum longus and by
the fibula; the branch passes along the lateral surface of the tibial
cartilage, continues lateral to the hypotarsus, then turns medially
before extending distally between Mm. abductor digiti IV and flexor
hallucis brevis, sending twigs into each of these muscles and a long
twig into M. lumbricalis before terminating nonmuscularly.

INDIVIDUAL VARIATION.--In T.p. 3L,R (fig. 11B), an extra branch arises
from the tibial nerve as a separate (fourth) division; it enters the
medial head of M. flexor perforatus digiti IV and also gives off a twig
that anastomoses with the posterior division (left leg) or with the
first branch of the posterior division (right leg). In T.p. 3R (fig.
11B), a large extra branch arises from the proximal part of the medial
division and passes medial and then deep to the medial head of M. flexor
perforatus digiti III, perforates the tendinous part of the medial head
of M. flexor perforatus digiti II, and joins the posterior division
(lateral to the medial head of M. flexor perforatus digiti III). A
similar branch is found in T.p. 3L except that it arises from the
proximal part of the posterior (rather than the medial) division. In
T.p. 3R (fig. 11B), the branch to M. gastrocnemius pars externa arises
so far proximally that it appears as a separate (fifth) division of the
tibial nerve. In two legs, the branch of the medial division that
supplies M. gastrocnemius pars media sends a twig into the distal end of
M. femorocruralis (fig. 11A).

_T. cupido_

INDIVIDUAL VARIATION.--In one leg, an extra branch of the medial
division arises immediately distal to the branch to M. gastrocnemius
pars media and enters the proximal end of the medial head of M. flexor
perforatus digiti III. In one instance, the branch to M. gastrocnemius
pars interna passes through a gap in the origin of M. plantaris rather
than distal to the origin of the latter.

_P. p. jamesi_

INDIVIDUAL VARIATION.--The branch to M. gastrocnemius pars interna gives
a minute twig to the deep surface of the free belly of M. plantaris in
one leg.

[Illustration: FIG. 2. Ventral views of the lumbosacral plexus of
_Tympanuchus pallidicinctus_. Sympathetic ganglionated chain removed.
Numbers indicate synsacral spinal nerves. × 2. A. T.p. 1L. B. T.p. 2L.]

[Illustration: FIG. 3. Ventral views of the lumbosacral plexus.
Sympathetic ganglionated chain removed. Numbers indicate synsacral
spinal nerves. × 2. A. _Tympanuchus cupido pinnatus_ 3L. B. _Pedioecetes
phasianellus jamesi_ 4L.]

[Illustration: FIG. 4. Semidiagrammatic ventral views of the femoral
nerve, showing the distribution of the branches. × 3. 1,2, M. extensor
iliotibialis anticus; 3, cutaneous; 4-6, M. extensor iliotibialis
lateralis; 7,8, M. iliacus; 9, M. gluteus profundus; 10-12, fused Mm.
vastus lateralis and vastus medialis; 13,14, M. vastus medialis; 15, M.
ambiens; 16, M. femoritibialis internus; 17, nonmuscular; 18, M. psoas;
19, M. iliotrochantericus medius. A. _Tympanuchus cupido pinnatus_ 3L.
B. _Pedioecetes phasianellus jamesi_ 3L.]

[Illustration: FIG. 5. Semidiagrammatic ventral views of the femoral
nerve, showing the distribution of the branches. × 3. 1,2, M. extensor
iliotibialis anticus; 3, cutaneous; 5,6, M. extensor iliotibialis
lateralis; 7,8, M. iliacus; 9, M. gluteus profundus; 10,11, fused Mm.
vastus lateralis and vastus medialis; 13, M. vastus medialis; 15, M.
ambiens; 16, M. femoritibialis internus; 17, nonmuscular; 18, M. psoas;
19, M. iliotrochantericus medius. A. _Tympanuchus pallidicinctus_ 2L. B.
_Tympanuchus cupido attwateri_ 1R.]

[Illustration: FIG. 6. Semidiagrammatic dorsolateral view of the sciatic
nerve of _Pedioecetes phasianellus jamesi_ 3R, showing the distribution
of the branches. × 2-1/2. 1, M. gluteus profundus; 2, M. piriformis; 3,
M. extensor iliotibialis lateralis; 4-7, M. extensor iliofibularis; 8,
M. flexor cruris medialis; 9, cutaneous; 10, to pudendal plexus; 11, M.
flexor cruris lateralis; 12, M. caudofemoralis pars caudifemoralis;
13-15, M. caudofemoralis pars iliofemoralis; 16,17, M. flexor
ischiofemoralis; 18,19, M. femorocruralis (branch of tibial nerve); 20,
cutaneous; 21, M. gastrocnemius pars media (branch of tibial nerve); 22,
cutaneous.]

[Illustration: FIG. 7. Semidiagrammatic dorsolateral view of the sciatic
nerve of _Tympanuchus pallidicinctus_ 2L, showing the distribution of
the branches. × 2-1/2. 1, M. gluteus profundus; 2, M. piriformis; 3, M.
extensor iliotibialis lateralis; 4, 7, M. extensor iliofibularis; 8, M.
flexor cruris medialis; 9, cutaneous; 10, to pudendal plexus; 11, M.
flexor cruris lateralis; 12, M. caudofemoralis pars caudifemoralis;
13-15, M. caudofemoralis pars iliofemoralis; 17, M. flexor
ischiofemoralis; 18, M. femorocruralis (branch of tibial nerve); 22,
cutaneous; 23, nonmuscular (branch of peroneal nerve).]

[Illustration: FIG. 8. Semidiagrammatic dorsolateral view of the sciatic
nerve of _Tympanuchus cupido pinnatus_ 3L, showing the distribution of
the branches. × 2-1/2. 1, M. gluteus profundus; 2, M. piriformis; 3, M.
extensor iliotibialis lateralis; 4,7, M. extensor iliofibularis; 8, M.
flexor cruris medialis; 9, cutaneous; 11, M. flexor cruris lateralis;
12, M. caudofemoralis pars caudifemoralis; 13, M. caudofemoralis pars
iliofemoralis; 17, M. flexor ischiofemoralis; 18, M. femorocruralis
(branch of tibial nerve); 20, cutaneous; 22, cutaneous.]

[Illustration: FIG. 9. Semidiagrammatic dorsolateral view of the sciatic
nerve of _Pedioecetes phasianellus jamesi_ 3L, showing the distribution
of the branches. × 2-1/2. 1, M. gluteus profundus; 2, M. piriformis; 3,
M. extensor iliotibialis lateralis; 4,5,7, M. extensor iliofibularis; 8,
M. flexor cruris medialis; 9, cutaneous; 11, M. flexor cruris lateralis;
13,14, M. caudofemoralis pars iliofemoralis; 16,17, M. flexor
ischiofemoralis; 18,19, M. femorocruralis (branch of tibial nerve); 20,
cutaneous; 22, cutaneous.]

[Illustration: FIG. 10. A,B. Semidiagrammatic drawings of the peroneal
nerve of _Tympanuchus pallidicinctus_ 1L, showing the distribution of
the branches. × 2. C. Semidiagrammatic drawing of the distal part of the
peroneal nerve of _Tympanuchus cupido attwateri_ 1R, showing the
distribution of the branches. × 2. 1,2, M. tibialis anticus (tibial
head); 3,4, M. tibialis anticus (femoral head); 5, M. extensor digitorum
longus; 6, nonmuscular; 7,8, M. peroneus longus; 9, M. peroneus brevis;
10,11, M. extensor hallucis longus (proximal head); 12, M. extensor
hallucis longus (distal head); 13-15, nonmuscular (to toes); 16, M.
abductor digiti II; 17, M. extensor brevis digiti III; 18, M. extensor
brevis digiti IV.]

[Illustration: FIG. 11. A,B. Semidiagrammatic drawings of the tibial
nerve (excluding the paraperoneal branch) of _Tympanuchus
pallidicinctus_, showing the distribution of the branches. × 2. A. T.p.
1L. B. T.p. 3R. C. Semidiagrammatic drawing of the distal part of the
paraperoneal branch of the tibial nerve of _Pedioecetes phasianellus
jamesi_ 2L, showing the distribution of the branches. × 2. 1, M.
femorocruralis; 2, M. gastrocnemius pars media; 3, M. popliteus; 4, M.
plantaris; 5, M. flexor digitorum longus; 6-8, nonmuscular; 9-11, M.
gastrocnemius pars interna; 12,13, M. flexor hallucis longus; 14-16, M.
flexor perforatus digiti IV (medial head); 17, M. flexor perforatus
digiti III (medial head); 18-20, M. flexor perforatus digiti II; 21, M.
flexor perforatus digiti IV (lateral head); 22-24, M. flexor perforatus
digiti IV (anterolateral head); 25, M. flexor perforatus digiti III
(anterolateral head); 26, M. flexor perforans et perforatus digiti III;
27,28, M. flexor perforans et perforatus digiti II; 29, M. gastrocnemius
pars externa; 30,31, M. abductor digiti IV; 32,33, M. flexor hallucis
brevis; 34,35, nonmuscular (to toes).]




MUSCLES


In the accounts of the muscles the name used by Hudson, _et al._ (1959)
for each muscle is given in parentheses after the name used by me if the
two differ.

In the account of each muscle, the description of the condition found in
most specimens of the Lesser Prairie Chicken (_T. pallidicinctus_) is
given first. This is hereafter referred to as the typical condition for
_T. pallidicinctus_. Then any individual variations found within this
species are given. Under the heading _T. cupido_ any constant
differences between this species and typical _T. pallidicinctus_ are
given first, and any individual variations found within the species _T.
cupido_ (both subspecies considered together) are given second. Under
the heading _P. p. jamesi_ any constant differences between this
subspecies and the typical condition for _T. pallidicinctus_ (thus these
differences are not necessarily constant between the two genera) are
given first, and any individual variations found within the subspecies
_P. p. jamesi_ are given second.

In the bird embryo, according to the studies of Romer (1927) and Wortham
(1948), the muscles within each segment of the leg differentiate from
distinct dorsal or ventral mesenchymal masses. Presumably these
represent the primitive dorsal extensor and ventral flexor muscle
masses. The list below indicates the ontogenetic origin of the avian leg
muscles, according to the studies of Romer and Wortham. The individual
muscles are discussed in the order in which they are listed below.

Dorsal muscles of thigh

    M. extensor iliotibialis lateralis      M. extensor iliofibularis
    M. extensor iliotibialis anticus        M. piriformis
    M. ambiens                              M. gluteus profundus
    M. vastus lateralis                     M. iliacus
    M. vastus medialis                      M. iliotrochantericus medius
    M. femoritibialis internus              M. psoas


Ventral muscles of thigh

    M. flexor cruris lateralis              M. adductor superficialis
    M. flexor cruris medialis               M. adductor profundus
    M. caudofemoralis                       M. obturator
    M. flexor ischiofemoralis               M. femorocruralis


Ventral muscles of shank

    M. gastrocnemius                        M. flexor perforatus digiti III
    M. flexor perforans et perforatus       M. flexor perforatus digiti II
       digiti II                            M. flexor hallucis longus
    M. flexor perforans et perforatus       M. plantaris
       digiti III                           M. flexor digitorum longus
    M. flexor perforatus digiti IV          M. popliteus


Dorsal muscles of shank

    M. peroneus longus                      M. extensor digitorum longus
    M. tibialis anticus                     M. peroneus brevis


Dorsal muscles of foot

    M. extensor hallucis longus             M. extensor proprius digiti III
    M. abductor digiti II                   M. extensor brevis digiti IV
    M. extensor brevis digiti III

Ventral muscles of foot

    M. lumbricalis                          (M. adductor digiti II--not
    M. abductor digiti IV                       present)
    M. flexor hallucis brevis               (M. adductor digiti IV--not
                                                present)

[Illustration: FIG. 12. _Tympanuchus pallidicinctus_ 2L. Lateral view of
the superficial muscles of the left leg. × 1.]

=_M. Extensor Iliotibialis Lateralis_= (M. iliotibialis), Figs. 12, 13,
20F, G

_T. pallidicinctus_

[Illustration: FIG. 13. _Tympanuchus pallidicinctus_ 2L. Medial view of
the superficial muscles of the left leg. × 1. Articular capsule shown by
concentrically arranged dashes.]

GENERAL DESCRIPTION AND RELATIONS.--Most superficial muscle on lateral
surface of thigh; broad, flat, and triangular; bounded anteriorly by M.
extensor iliotibialis anticus and posteriorly by M. flexor cruris
lateralis; posterior part considerably thicker than anterior part;
anteroproximal and centrodistal parts aponeurotic; extreme
posteroproximal corner also aponeurotic (could be considered tough sheet
of connective tissue intimately fused with M. extensor iliotibialis
lateralis, rather than part of muscle itself; see fig. 20F); latter
aponeurosis, as well as adjacent fleshy fibers, overlapped by M. flexor
cruris lateralis; this aponeurosis fused with posterior end of
underlying M. caudofemoralis pars iliofemoralis; centrodistal
aponeurosis tightly fused to underlying Mm. vastus lateralis and vastus
medialis; fleshy fibers posterior to this aponeurosis also fused with M.
vastus lateralis, although posterior third of muscle free; fleshy part
anterior to this aponeurosis bound by tough connective tissue to
underlying M. vastus medialis, although no fusion of fibers; anterior
edge tightly bound by strong connective tissue to M. extensor
iliotibialis anticus, with some fusion of fibers (proximally);
posteroproximal corner bound by tough connective tissue to adjacent
muscles; anteroproximal aponeurosis fused with aponeurotic
anteroproximal part of underlying M. extensor iliofibularis. Continuous
proximal aponeurosis of M. extensor iliotibialis anticus and of M.
extensor iliotibialis lateralis underlain by tough fascial sheet
overlying M. gluteus profundus; anterior part of this fascia tightly
fused to latter muscle but free from overlying aponeurosis; posterior
part of this fascia tightly fused to overlying aponeurosis but free from
M. gluteus profundus; middle part of fascia fused to both aponeurosis
and M. gluteus profundus.

[Illustration: FIG. 14. _Tympanuchus pallidicinctus_ 2L. Lateral view of
the muscles of the left leg. The following muscles have been removed:
extensor iliotibialis lateralis, extensor iliotibialis anticus,
gastrocnemius pars externa and pars interna, and peroneus longus. × 1.]

[Illustration: FIG. 15. _Tympanuchus pallidicinctus_ 2L. Medial view of
the muscles of the left leg. The following muscles have been removed:
extensor iliotibialis lateralis, extensor iliotibialis anticus, ambiens,
flexor cruris lateralis (in part), flexor cruris medialis (in part),
gastrocnemius pars externa and pars interna, and peroneus longus. × 1.]

ORIGIN.--Approximately the anterior half attaches by an extensive
aponeurosis, which is continuous anteriorly with that of M. extensor
iliotibialis anticus, to the anterior iliac crest, ending posteriorly at
the anterior end of the lateral iliac process; the posterior part
attaches fleshily to the edge of the entire lateral iliac process and
(posterior few mm.) aponeurotically to the entire lateral ischiatic
ridge. The proximal part of the belly is much thicker than the fleshy
origin. Two accessory aponeuroses associate with the anterior part of
the muscle; the proximal one of these comes off the deep surface several
mm. distal to the proximal end of the fleshy belly and passes medially
between Mm. gluteus profundus and iliacus, fusing to both these muscles,
and attaches to the lateral edge of M. iliotrochantericus medius and to
the lateral edge of the ilium anterior to the latter; the aponeurosis
actually splits into two sheets at the edge of M. iliotrochantericus
medius; these sheets fuse to the dorsal and ventral surfaces of the
latter muscle, enclosing it; the part of this aponeurosis between Mm.
iliacus and iliotrochantericus medius is strongly fused with the
underlying body wall. The distal accessory aponeurosis (sometimes weak)
comes off the deep surface several mm. distal to the proximal one and
passes medially along the ventral surface of M. iliacus, fusing with the
latter, then joining the proximal accessory aponeurosis medial to M.
iliacus.

INSERTION.--The muscle inserts by a broad aponeurosis strongly fused to
the underlying Mm. vastus lateralis and vastus medialis; the aponeurosis
contributes superficially to the patellar tendon, attaching to the
lateral half of the rotular crest.

[Illustration: FIG. 16. _Tympanuchus pallidicinctus_ 2L. Lateral view of
the muscles of the left leg. The following muscles, in addition to those
listed for Fig. 14, have been removed: ambiens, vastus lateralis pars
lateralis, vastus medialis (except for part of patellar tendon),
extensor iliofibularis, flexor cruris lateralis (in part), flexor
perforans et perforatus digiti II, and flexor perforans et perforatus
digiti III. × 1.]

INNERVATION.--A variable number of branches (usually two) of the middle
division of the femoral nerve pass ventral to M. iliacus and between Mm.
extensor iliotibialis anticus and vastus medialis and enter the deep
surface of the anteroproximal part of the muscle. The branch of the
middle peroneal division of the sciatic nerve emerges between the
proximal ends of Mm. extensor iliofibularis and vastus lateralis and
sends twigs into the deep surface of M. extensor iliotibialis lateralis.

INDIVIDUAL VARIATION.--In two legs, the nerve supplying M. extensor
iliotibialis anticus gives twigs into M. extensor iliotibialis
lateralis.

_T. cupido_

DIFFERENCES FROM _T. pallidicinctus_.--The fleshy origin from the
lateral iliac process is considerably thicker (reflected in a thicker
lateral iliac process).

INDIVIDUAL VARIATION.--In three legs the nerve supplying M. extensor
iliotibialis anticus gives twigs into M. extensor iliotibialis
lateralis. In another leg one of the branches to the fused Mm. vastus
lateralis and vastus medialis sends a twig into M. extensor iliotibialis
lateralis.

[Illustration: FIG. 17. _Tympanuchus pallidicinctus_ 2L. Lateral view of
the muscles of the left leg. The following muscles, in addition to those
listed for Fig. 16, have been removed: vastus lateralis pars postica,
gluteus profundus, flexor cruris medialis (in part), caudofemoralis,
flexor perforatus digiti IV, and tibialis anticus. × 1.]


_P. p. jamesi_

[Illustration: FIG. 18. _Tympanuchus pallidicinctus_ 2L. Lateral view of
the muscles of the left leg. The following muscles, in addition to those
listed for Fig. 17, have been removed: patellar tendon, iliacus,
iliotrochantericus medius, flexor cruris lateralis, flexor cruris
medialis, flexor ischiofemoralis, adductor superficialis,
femorocruralis, gastrocnemius pars media, flexor perforatus digiti III,
flexor perforatus digiti II, flexor hallucis longus, plantaris, flexor
digitorum longus, popliteus, and extensor digitorum longus. × 1.]

DIFFERENCES FROM TYPICAL _T. pallidicinctus_.--The posteroproximal
aponeurosis is more extensive, resulting in a narrower proximal fleshy
end (fig. 20G); the fleshy fibers adjacent to this aponeurosis are not
overlapped by M. flexor cruris lateralis. There is a fusion of fibers
between the anterodistal fleshy part of M. extensor iliotibialis
lateralis and the underlying M. vastus medialis, but there is no fusion
of fibers between the anterior edge of M. extensor iliotibialis
lateralis and M. extensor iliotibialis anticus. The connective tissue
binding the posteroproximal corner to adjacent muscles is stronger. The
fleshy part of the origin is narrower, partly tendinous, and much
thinner (reflected in a thin lateral iliac process). The proximal border
is much more nearly straight, owing to a less pronounced lateral iliac
process. The distal accessory aponeurosis is absent.

[Illustration: FIG. 19. _Tympanuchus pallidicinctus_ 2L. A. Posterior
view of the muscles of the left shank. The following shank muscles, in
addition to those listed for Fig. 17, have been removed: gastrocnemius
pars media, flexor perforatus digiti III, and flexor perforatus digiti
II. × 1. B. Posterior view of the proximal end of the shank, showing the
most deeply situated muscle. × 1. C. Lateral view of the head of the
left femur and the middle part of the pelvis, showing the deepest part
of M. obturator. × 1. D. Medial view of the posteroventral part of the
left side of the pelvis, showing the intrapelvic part of M. obturator. ×
1. E. Anterior view of the left tarsometatarsus, showing the dorsal
intrinsic muscles of the foot. × 1-1/2. F. Posterior view of the left
tarsometatarsus, showing the ventral intrinsic muscles of the foot. ×
1-1/2.]

INDIVIDUAL VARIATION.--The muscle is usually somewhat fused to the
posteroproximal and anteroproximal fleshy corners of the underlying M.
extensor iliofibularis.


=_M. Extensor Iliotibialis Anticus_= (M. sartorius), Figs. 12, 13

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Anteriormost muscle of thigh; long
and strap-shaped; proximal part entirely anterior (adjacent) to M.
extensor iliotibialis lateralis; posterior edge of middle part medial to
latter muscle; distal part mostly medial to Mm. extensor iliotibialis
lateralis and vastus medialis; proximal part aponeurotic, continuous
posteriorly with anteroproximal aponeurosis of M. extensor iliotibialis
lateralis; anterior edge of M. extensor iliotibialis lateralis bound by
strong connective tissue to adjacent part of M. extensor iliotibialis
anticus; some fusion of fibers (proximally) between these two muscles;
anteroproximal corner of fleshy part of muscle sometimes fused to
underlying anterior edge of ilium and fascia covering body wall
musculature adjacent (anterior) to ilium.

ORIGIN.--The muscle arises aponeurotically from the anterior part of the
anterior iliac crest and (anteroproximal corner) from the anterior end
of the median dorsal ridge.

INSERTION.--The flat tendon, continuous posteriorly with the superficial
tendon of M. femoritibialis internus, fuses to the tendon of M. vastus
medialis, contributing superficially to the medial part of the patellar
tendon, which attaches to the medial half of the rotular crest; most of
the tendon is overlapped by the edge of M. gastrocnemius pars interna.

INNERVATION.--A branch of the anterior division of the femoral nerve
gives twigs into the lateral surface of the posterior part.

INDIVIDUAL VARIATION.--In two legs, a twig from the anteriormost branch
of the middle division of the femoral nerve anastomoses with the typical
branch to M. extensor iliotibialis anticus.

_T. cupido_

INDIVIDUAL VARIATION.--In several legs, the anterior edge of origin
extends forward onto the neural spine of the last free thoracic
vertebra. A twig from the middle division of the femoral nerve
anastomoses with the typical branch to M. extensor iliotibialis anticus
in three legs.

_P. p. jamesi_

DIFFERENCES FROM TYPICAL _T. pallidicinctus_.--There is no fusion of
fibers between M. extensor iliotibialis anticus and M. extensor
iliotibialis lateralis.

INDIVIDUAL VARIATION.--The anterior edge of origin extends forward onto
the neural spine of the last free thoracic vertebra in some legs.

[Illustration: FIGURE 20. Explanation on opposite page.]

EXPLANATION OF FIGURE 20

A-D. Dorsal views of M. iliotrochantericus medius, showing its
relationship to femoral notch. × 1. In D, note absence of femoral notch
and location of branch of femoral nerve. A. _Tympanuchus pallidicinctus_
2L. B. _T. cupido pinnatus_ 4L. C. _Pedioecetes phasianellus jamesi_ 1L.
D. _T. pallidicinctus_ 3L.

E. Medial view of distal end of M. flexor cruris medialis of _P. p.
jamesi_ 4L. × 1. Part of insertion is covered by medial collateral
ligament.

F,G. Lateral views of posteroproximal corner of M. extensor iliotibialis
lateralis (removed from specimen). × 1. F. _T. pallidicinctus_ 2L. G.
_P. p. jamesi_ 3L.

H,I. Dorsolateral views of M. piriformis. × 1. H. _P. p. jamesi_ 1L. I.
_T. cupido attwateri_ 1L.

J. Lateral view of M. caudofemoralis pars caudifemoralis (removed from
specimen) of _T. c. pinnatus_ 4L. × 1.

K. Lateral view of extrapelvic part of M. obturator of _T.
pallidicinctus_ 3L (bones not shown). × 2.

L,M. Region surrounding obturator foramen of _T. pallidicinctus_ 3L,
showing points of attachment of three parts of M. obturator (muscles
removed). × 3. L. Lateral view. M. Medial view.

N. Anterior view of left tarsometatarsus of _P. p. jamesi_ 4L, showing
dorsal intrinsic muscles of foot. × 1-1/2. Tendon of M. extensor
digitorum longus has been removed.


=_M. Ambiens_=, Figs. 13, 16, 17

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Thin and elongate; on medial surface
of thigh; broadest above middle of belly; belly narrowed distally,
forming long slender tendon passing lateral to distal part of M.
extensor iliotibialis anticus; bounded anterolaterally by M. vastus
medialis and posterolaterally by Mm. femoritibialis internus and psoas
(proximally).

ORIGIN.--The muscle arises by a short flat tendon from the pectineal
process.

INSERTION.--The long slender tendon enters an elongate channel within
the patellar tendon; the point of entrance is at the proximal end of the
latter tendon just medial to the patella; the tendon passes
distolaterally (within the channel) below the patella and emerges from
the distolateral edge of the patellar tendon and then extends distally
along the anterolateral surface of the head of the fibula, superficial
to the fibular arm of the guide loop for M. extensor iliofibularis, and
joins the anterolateral surface of the common tendon of origin of the
anterolateral heads of Mm. flexor perforatus digiti III, flexor
perforatus digiti IV, and flexor perforatus digiti II; the point of
junction is usually immediately proximal to the proximal end of the
lateral head of M. flexor digitorum longus.

INNERVATION.--The branch of the middle division of the femoral nerve
that supplies M. femoritibialis internus gives off a tiny twig or twigs
that penetrate the lateral surface of the proximal part of M. ambiens.

INDIVIDUAL VARIATION.--None of significance in _T. pallidicinctus_ or in
_P. p. jamesi_; in _T. cupido_ the origin is partly fleshy in one leg.


=_M. Vastus Lateralis_= (M. femoritibialis externus + part of M.
femoritibialis medius), Figs. 14, 16

Fisher and Goodman (1955) apply the name femoritibialis externus to the
muscle unit that I here term the pars postica of M. vastus lateralis.
The reasons for this change are discussed in the section on terminology.

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Thick; on lateral surface of femur
deep to M. extensor iliotibialis lateralis; anterior to M. extensor
iliofibularis and lateral to M. vastus medialis; much of lateral
surface, except proximal part, fused with overlying M. extensor
iliotibialis lateralis; deep surface of anterior half fused with M.
vastus medialis; proximal part overlapping, but usually not fusing with,
insertions of Mm. iliacus and caudofemoralis; partially separable into
two parts--pars lateralis and pars postica, former constituting main
part of muscle; latter considerably smaller and situated deep to
posterodistal part of pars lateralis, except for posterodistal part
extending posterior to edge of pars lateralis; proximal part of pars
postica strongly fused with pars lateralis; posterodistal tendinous edge
of pars lateralis fused or not fused with lateral surface of pars
postica; proximal end (narrow) of pars postica tendinous and variable in
length.

ORIGIN.--_Pars lateralis_: This arises fleshily from most of the lateral
surface and (distally) from the anterior surface of the femur, extending
anteriorly to the anterior intermuscular line, fusing with M. vastus
medialis, and extending posteriorly to the posterolateral intermuscular
line (proximally) and the origin of pars postica (distally); the
proximal end begins at the level of the distal edge of the insertion of
M. iliotrochantericus medius, contacting the insertions of Mm.
iliotrochantericus medius, piriformis, and flexor ischiofemoralis, and
terminates distally at the level of the proximal ends of the femoral
condyles.

_Pars postica_: This arises fleshily and tendinously (proximal end and
deep surface) from the posterolateral surface of approximately the
distal half of the femur, extends posteromedially to the posterolateral
intermuscular line where it contacts the origin of M. femorocruralis,
and extends anteriorly to the level of a line drawn diagonally across
the femur from the proximal end of the origin (at the posterolateral
intermuscular line) to the proximal end of the external condyle; the
distal end is anterior (adjacent) to the attachment of the proximal arm
of the tendinous guide loop for M. extensor iliofibularis; the origin is
adjacent to, but distinct from, the origin of pars lateralis.

INSERTION.--_Pars lateralis_ is fused indistinguishably with M. vastus
medialis; these two muscles form the main (middle) part of the patellar
tendon, which also receives contributions from pars postica and Mm.
femoritibialis internus, extensor iliotibialis lateralis, and extensor
iliotibialis anticus; the patellar tendon attaches to the entire rotular
crest of the tibia; the patella is situated in the proximal part of this
tendon; some deep fleshy fibers of M. vastus lateralis pars lateralis
and M. vastus medialis attach to the proximal edge of the patella. _Pars
postica_ forms a short narrow tendon that fuses to the lateral part of
the tendon of pars lateralis, forming the lateralmost part of the
patellar tendon. A broad flat vinculum extends from the lateral surface
of the femorofibular fascia (defined under M. flexor perforans et
perforatus digiti II) to the deep surface of the lateral part of the
patellar tendon; a similar vinculum extends from the medial surface of
the internal condyle to the deep surface of the medial part of the
patellar tendon.

INNERVATION.--Two or more branches of the middle division of the femoral
nerve penetrate the anterior surface of the fused Mm. vastus lateralis
(pars lateralis) and vastus medialis; short twigs emerge from the deep
surface of pars lateralis and penetrate the superficial surface of the
anteroproximal part of pars postica.

INDIVIDUAL VARIATION.--The proximal ends of M. vastus medialis and M.
vastus lateralis are usually separated by a deep notch. In some legs, a
small bundle of fibers forming the anteroproximal part of M. vastus
lateralis attaches to the lateral surface of M. vastus medialis anterior
to this notch.

_T. cupido_

INDIVIDUAL VARIATION.--One leg shows the same variation found in _T.
pallidicinctus_ (see above). In several legs, pars lateralis does not
extend so far proximally as usual, but begins at the level of insertion
of M. piriformis (does not contact the insertion of M.
iliotrochantericus medius) and may not overlap M. iliacus. In a few
legs, no vincula are associated with the patellar tendon.

_P. p. jamesi_

INDIVIDUAL VARIATION.--Pars lateralis often begins proximally at the
level of the insertion of M. piriformis.


=_M. Vastus Medialis_= (Part of M. femoritibialis medius), Figs. 13, 14,
15

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Thick; on anteromedial surface of
femur medial to anterior part of M. vastus lateralis pars lateralis;
bounded medially by Mm. ambiens and extensor iliotibialis anticus
(distally); bounded posteromedially by M. femoritibialis internus;
proximal part medial to posterior ends of Mm. iliacus,
iliotrochantericus medius, and gluteus profundus; lateral surface,
except proximal part, fused with anterior part of M. vastus lateralis
pars lateralis; part of lateral surface of M. vastus medialis covered by
sheet of fascia attaching to anterior intermuscular line; M. vastus
lateralis separable from this fascia, but fascia absent anteriorly and
distally and these two muscles indistinguishably fused.

ORIGIN.--The proximal third is attached narrowly by its lateral edge;
the distal two thirds is attached broadly by its entire deep surface.
The proximal third arises tendinously from the trochanteric ridge and
the proximal end of the anterior intermuscular line and fleshily from a
narrow area of the femur adjacent (medial) to the latter; the distal
part arises tendinously from the anterior intermuscular line and
fleshily from a broad adjacent area on the anteromedial surface of the
femur, terminating distally at the level of the proximal end of the
internal condyle; the posterior edge contacts the origin of M.
femoritibialis internus.

INSERTION.--Attachment is in common with M. vastus lateralis pars
lateralis, which see.

INNERVATION.--Two or more branches of the middle division of the femoral
nerve penetrate the anterior surface of the fused Mm. vastus medialis
and vastus lateralis pars lateralis; a variable number of branches of
the same division penetrate the medial surface of the proximal part of
M. vastus medialis.

INDIVIDUAL VARIATION.--None of significance in any of the three species
studied.


=_M. Femoritibialis Internus_=, Figs. 13, 15

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Elongate; on posteromedial surface
of femur; bounded anteriorly by M. vastus medialis and posteriorly by M.
adductor profundus (overlapping anterior edge of latter); anteroproximal
part lateral to M. ambiens; anterodistal corner deep to distal end of M.
extensor iliotibialis anticus; distal part of muscle split into
superficial and deep layers; superficial layer thin, narrow, and
tendinous except for proximal end; deep layer wider, much thicker, and
fleshy except for distal end taking form of flat tendon; anterior edge
of latter somewhat fused to medial edge of tendon of M. vastus medialis;
deep layer widest near distal end of fleshy part; posterior edge of
superficial layer fused to underlying deep layer, and anterior edge
fused to (continuous with) posterior edge of tendon of M. extensor
iliotibialis anticus.

ORIGIN.--The origin is mostly fleshy from the posteromedial surface of
the femur between the origin of M. vastus medialis and the posterior
intermuscular line, terminating immediately proximal to the internal
condyle.

INSERTION.--The tendons of both superficial and deep layers attach to
the medial part of the rotular crest, forming the medialmost part of the
patellar tendon.

INNERVATION.--The posteriormost branch of the middle division of the
femoral nerve penetrates the medial surface of the muscle near the
proximal end.

INDIVIDUAL VARIATION.--None of significance in any of the three species
studied.


=_M. Extensor Iliofibularis_= (M. biceps femoris), Figs. 12, 14, 16, 17

The term extensor in the name of this muscle does not refer to its
function. Howell (1938) used the term extensor to indicate derivation of
the muscle from the primitive dorsal extensor muscle mass. (Likewise he
used the term flexor to indicate derivation from the primitive ventral
flexor muscle mass.)

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Deep to M. extensor iliotibialis
lateralis and posterior to femur; broad proximally and narrow distally;
posterior to M. vastus lateralis and anterior to proximal part of M.
flexor cruris lateralis (superficial to distal part of latter);
anteroproximal part aponeurotic, fused to deep surface of aponeurosis of
M. extensor iliotibialis lateralis; proximal part of aponeurosis of M.
extensor iliofibularis also fused to dorsal edges of underlying Mm.
gluteus profundus and piriformis.

ORIGIN.--The posterior part is fleshy from the ventromedial surface of
the entire lateral iliac process; the anterior part is aponeurotic from
the posterior part of the anterior iliac crest.

INSERTION.--The tendon forms along the posterodistal edge of the belly
and continues beyond the end of the belly as a cylindrical tendon that
passes through the tendinous guide loop (the belly terminates
approximately at the level of the guide loop), then extends
anterodistally into the shank musculature; the tendon passes between the
medial and lateral heads of M. flexor perforatus digiti IV, between the
medial and lateral heads of M. flexor perforatus digiti II, lateral to
the common tendon of the anterolateral heads of Mm. flexor perforatus
digiti IV, flexor perforatus digiti II, and flexor perforatus digiti
III, and between the posterior and lateral heads of M. flexor digitorum
longus, attaching to the fibular tubercle.

The tendinous guide loop has three arms--proximal femoral, distal
femoral, and fibular; the proximal and distal femoral arms unite
posterior to the tendon of M. extensor iliofibularis; the proximal arm
is medial to, and the distal arm is lateral to, the latter; the fibular
arm joins the distal edge of the distal arm lateral to the tendon of M.
extensor iliofibularis. The proximal arm extends anteroproximally
lateral to the medial head of M. flexor perforatus digiti IV and medial
to M. vastus lateralis pars postica, attaching to a narrow line on the
anterolateral surface of the femur a short distance proximal to the
external condyle and adjacent (posterior) to the origin of M. vastus
lateralis pars postica. The distal arm extends anteriorly medial to the
posterior head of M. flexor perforans et perforatus digiti II and medial
to M. vastus lateralis pars postica, attaching in common with the tendon
of origin of M. gastrocnemius pars externa to a small oval area on the
posterolateral surface of the femur a short distance proximal to the
fibular groove; the arm is also fused to the underlying articular
capsule. The fibular arm (broadest of the three) passes deep to, and
fused with, the common tendon of origin of the lateral heads of Mm.
flexor perforatus digiti IV and flexor perforatus digiti II, superficial
to the common tendon of origin of the anterolateral heads of Mm. flexor
perforatus digiti IV, flexor perforatus digiti II, and flexor perforatus
digiti III, and deep to the tendon of M. ambiens, attaching broadly to a
narrow line on the anterolateral surface of the proximal part of the
fibula; the arm is also fused to the underlying articular capsule.

INNERVATION.--A branch of the middle peroneal division of the sciatic
nerve sends twigs to the deep surface of the anteroproximal part; the
dorsal peroneal division of the sciatic nerve penetrates the deep
surface of the proximal end.

INDIVIDUAL VARIATION.--In some instances a variable number of twigs
arises from the peroneal nerve near the middle of the thigh and enters
the deep surface of the muscle. They are difficult to expose without
breaking and may have been overlooked in some specimens.

_T. cupido_

INDIVIDUAL VARIATION.--The same variation is found as in _T.
pallidicinctus_ (see above). In one leg, the tendon of insertion
bifurcates into proximal and distal arms before attaching.

_P. p. jamesi_

DIFFERENCES FROM TYPICAL _T. pallidicinctus_.--It arises from the
ventral rather than the ventromedial surface of the lateral iliac
process (there is no ventromedial surface to this process).

INDIVIDUAL VARIATION.--In nearly all of the legs, minute twigs to M.
extensor iliofibularis come off the peroneal nerve near the middle of
the thigh. The insertional tendon tends toward doubleness in two legs.


=_M. Piriformis_= (M. gluteus medius et minimus), Figs. 16, 20H, I

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Small, thin, and triangular; lateral
to antitrochanter and posterior part of trochanter; deep to M. extensor
iliofibularis and posterior (adjacent) to M. gluteus profundus; distal
half (or more) tendinous.

ORIGIN.--The muscle arises fleshily from the posterior end of the
anterior iliac crest (ventral to the origins of Mm. extensor
iliotibialis lateralis and extensor iliofibularis) beginning adjacent to
the posterior end of M. gluteus profundus.

INSERTION.--The flat tendon narrows, overlaps the anteroproximal corner
of insertion of M. flexor ischiofemoralis, and attaches to the lateral
surface of the proximal part of the femur immediately anterior to the
insertion of M. flexor ischiofemoralis and posterior to the proximal end
of M. vastus lateralis; the attachment is posterodistal to the insertion
of M. iliotrochantericus medius and posteroproximal to the insertion of
M. iliacus.

INNERVATION.--The small anterior peroneal division of the sciatic nerve
turns anteriorly immediately after emerging from the ilio-ischiatic
fenestra and passes deep to M. piriformis, giving twigs to the deep
surface.

INDIVIDUAL VARIATION.--In both legs of one specimen, the insertion does
not overlap the insertion of M. flexor ischiofemoralis. The
posteroproximal corner of the muscle is tendinous in one leg.

_T. cupido_

INDIVIDUAL VARIATION.--The anterior border is somewhat fused with the
posterior edge of M. gluteus profundus in one leg, while in another
there is a slight gap between the origins of M. gluteus profundus and M.
piriformis. In one leg, the posterior edge of the origin is aponeurotic.
On both sides of one specimen, an accessory tendinous band arises
several mm. posterior to the main part of M. piriformis and joins the
proximal part of the insertional tendon, thus forming a Y-shaped unit
(fig. 20I); the accessory tendon arises from the anterior end of the
lateral iliac process (left side) or from the anterior part of the
lateral iliac fossa (right side). The insertion may be proximal (rather
than posterior) to the proximal end of M. vastus lateralis. In one leg,
the insertional tendon is partly fused to the insertional tendon of M.
flexor ischiofemoralis.

_P. p. jamesi_

INDIVIDUAL VARIATION.--There is often a gap between the origins of M.
gluteus profundus and M. piriformis. In one leg (fig. 20H), the
posteroproximal corner of the muscle is aponeurotic. The insertion is
often proximal (rather than posterior) to the proximal end of M. vastus
lateralis. In one instance, the insertion does not overlap the insertion
of M. flexor ischiofemoralis.


=_M. Gluteus Profundus_= (M. iliotrochantericus posterior), Figs. 14, 16

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Large and thick; covering
dorsolateral surface of entire preacetabular part of ilium; deep to Mm.
extensor iliotibialis lateralis and extensor iliotibialis anticus;
bounded posteriorly by M. piriformis and ventrally by M. iliacus;
ventral edge fused with anterior part of latter and with proximal
accessory aponeurosis of M. extensor iliotibialis lateralis; tough sheet
of fascia strongly fused to anterior two thirds of lateral surface;
posterior to this, fascia overlying muscle but not attaching to it;
posterior half of fascia fused to overlying aponeurosis of M. extensor
iliotibialis lateralis; deep surface of muscle somewhat fused to
proximal part of M. iliotrochantericus medius.

ORIGIN.--The superficial surface is tendinous from the entire anterior
iliac crest except the posterior end and from the crest forming the
anterior and anterolateral edges of the ilium; the muscle arises
fleshily from the entire dorsolateral surface of the preacetabular ilium
as far posteriorly as the level of the pectineal process; the dorsal
edge is adjacent (anterior) to the origin of M. piriformis.

INSERTION.--The attachment is by a short, wide, thick tendon to a curved
line (convex anteriorly) on the lateral surface of the femoral
trochanter.

INNERVATION.--The anterodorsal division of the femoral nerve turns
dorsally through the femoral notch of the ilium and penetrates the deep
surface of the ventral part of the muscle midway of its length; the
anterior peroneal division of the sciatic nerve passes deep to M.
piriformis and terminates near the posterodorsal edge of M. gluteus
profundus.

INDIVIDUAL VARIATION.--On both sides of one specimen, the branch from
the femoral nerve passes lateral to the extreme anteroproximal corner of
M. iliotrochantericus medius instead of through the femoral notch.

_T. cupido_

INDIVIDUAL VARIATION.--In one leg, the insertional tendon is strongly
fused to the insertional tendon of M. iliotrochantericus medius.

_P. p. jamesi_

INDIVIDUAL VARIATION.--None of significance.


=_M. Iliacus_= (M. iliotrochantericus anterior), Figs. 13, 14, 15, 16,
17

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Adjacent ventrally to ventrolateral
edge of M. gluteus profundus; lateral edge much thicker than medial
edge; deep to M. extensor iliotibialis lateralis and anterolateral to M.
iliotrochantericus medius; distal (posterior) end passing between
proximal ends of Mm. vastus medialis and vastus lateralis pars
lateralis; insertion overlapped by latter; dorsal surface of anterior
part fused with ventrolateral edge of M. gluteus profundus and with
ventral surface of proximal accessory aponeurosis of M. extensor
iliotibialis lateralis; ventral surface partly fused with distal
accessory aponeurosis of latter muscle.

ORIGIN.--The origin is fleshy and tendinous from the lateral edge of the
anterior part of the ilium.

INSERTION.--The attachment is by a short flat tendon to the lateral
surface of the femur distal to the trochanter and anterodistal to the
insertion of M. piriformis and deep to the proximal part of M. vastus
lateralis pars lateralis.

INNERVATION.--The dorsal division of the femoral nerve penetrates the
ventral surface.

INDIVIDUAL VARIATION.--The dorsal division of the femoral nerve may fuse
proximally with either the anterior or middle division. In one leg,
there are two separate branches to the muscle.

_T. cupido_

INDIVIDUAL VARIATION.--The insertion may not be overlapped by M. vastus
lateralis. The dorsal division of the femoral nerve is fused proximally
with the middle division in one leg.

_P. p. jamesi_

DIFFERENCES FROM TYPICAL _T. pallidicinctus_.--The fleshy origin is
wider.

INDIVIDUAL VARIATION.--The dorsal division of the femoral nerve may fuse
proximally with either the anterior or middle division. In one leg,
there are two branches to M. iliacus, one fused with the anterior
division and the other with the middle division.


=_M. Iliotrochantericus Medius_=, Figs. 17, 20A, B, C, D

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Small and triangular; ventral to
posterior half of M. gluteus profundus; all but posteroventral corner
deep to latter; posteromedial to M. iliacus, anterior to neck of femur,
and dorsolateral (adjacent proximally) to M. psoas; proximal end notched
at level of femoral notch for passage of anterodorsal division of
femoral nerve; part anterior to femoral notch mainly tendinous; dorsal
surface of proximal part somewhat fused to M. gluteus profundus,
proximal accessory aponeurosis of M. extensor iliotibialis lateralis
split into two sheets enclosing and fusing with M. iliotrochantericus
medius, ultimately attaching to lateral edge of ilium in common with
origin of latter muscle.

ORIGIN.--The muscle arises from the ventrolateral surface of the ilium
anterior to the acetabulum and posterior to the origin of M. iliacus;
the anterior part attaches to the ventrolateral edge of the ilium and
the posterior part attaches just above the ventral edge. The muscle is
not attached to the concavity of the femoral notch (the origin is
notched here). The part attaching anterior to the femoral notch is
narrow, tendinous, and continuous anteriorly with the accessory
aponeurosis of M. extensor iliotibialis lateralis (thus the anterior
border of the muscle cannot be exactly delimited). The part attaching
posterior to the femoral notch is wider and fleshy (fig. 20A).

INSERTION.--The short flat tendon attaches to the lateral surface of the
distal end of the trochanter slightly anterior and immediately distal to
the insertion of M. gluteus profundus; the attachment is proximal to the
origin of M. vastus lateralis, anteroproximal to the insertion of M.
piriformis, and several mm. proximal to the insertion of M. iliacus.

INNERVATION.--The small posterodorsal division of the femoral nerve
penetrates the ventral surface.

INDIVIDUAL VARIATION.--On both sides of one specimen, the femoral notch
is absent and the proximal end of the muscle is not notched; the
proximal part is entirely fleshy and the anterior border is well defined
(fig. 20D).

_T. cupido_

INDIVIDUAL VARIATION.--The part attaching anterior to the femoral notch
has a fleshy origin in one leg (fig. 20B), but in another, no part
attaches anterior to the femoral notch (thus the muscle is not notched).
In one leg, the insertional tendon is strongly fused to, and continuous
with, the ventral edge of the insertional tendon of M. gluteus
profundus.

_P. p. jamesi_

INDIVIDUAL VARIATION.--The part attaching anterior to the femoral notch
may be mainly or entirely fleshy. In one leg, the part attaching
anterior to the femoral notch is entirely separate from, although
overlapped by, the main part of the muscle for the entire length of the
fleshy belly (fig. 20C); both parts have a common insertional tendon.


=_M. Psoas_= (M. iliacus), Figs. 13, 15, 18

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Small and slender; on medial aspect
of proximal end of thigh lateral to proximal end of M. ambiens;
ventromedial to M. iliotrochantericus medius; proximal end visible from
inside pelvis (medial to inguinal ligament); passes dorsolateral to
inguinal ligament.

ORIGIN.--The muscle arises fleshily from the ventrolateral edge of the
ilium posterior to the femoral notch and ventral (adjacent) to the
origin of M. iliotrochantericus medius.

INSERTION.--The attachment is tendinous to the medial surface of the
femur a short distance proximal to the origin of M. femoritibialis
internus.

INNERVATION.--The posterior division of the femoral nerve, which spirals
completely around M. psoas, gives several twigs into the proximal part.

INDIVIDUAL VARIATION.--None of significance.

_T. cupido_

INDIVIDUAL VARIATION.--In two legs the insertion is partly fleshy.

_P. p. jamesi_

INDIVIDUAL VARIATION.--In one leg the insertion is partly fleshy. The
posterior division of the femoral nerve perforates the muscle in one
instance.


=_M. Flexor Cruris Lateralis_= (M. semitendinosus), Figs. 12, 13, 14,
15, 16, 17

This muscle represents only the main head of the muscle for which Fisher
and Goodman (1955) used the same name. Their accessory head of M. flexor
cruris lateralis is here termed M. femorocruralis.

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Large, thick, and strap-shaped; on
posterior surface of thigh; proximal part bounded anteriorly by Mm.
extensor iliotibialis lateralis and extensor iliofibularis; anterodistal
part deep to latter; bounded medially by Mm. caudofemoralis (proximally)
and flexor cruris medialis (distally); proximal end much narrower than
remainder and posterior to ilium; fused to underlying tough membrane,
which forms body wall posterior to ilium; proximal half of narrow part
aponeurotic; distal part of muscle posterior to M. femorocruralis;
separated from latter by common raphe to which both attach; caudal
muscle (M. transversoanalis) attached aponeurotically to superficial
surface of posteroproximal fleshy part of M. flexor cruris lateralis.

ORIGIN.--The origin is tendinous (superficial surface) and fleshy from
the entire dorsolateral iliac ridge and fleshy from an area of the ilium
below this ridge, also tendinous from the posterior edge of the ilium
medial to the dorsolateral iliac ridge, and also tendinous from the
transverse processes of the first free caudal vertebra and the vertebra
either anterior or posterior to the latter.

INSERTION.--M. flexor cruris lateralis and M. femorocruralis insert
broadly on opposite sides of a long tendinous raphe that extends
parallel to, but some distance posterior to, the distal half of the
femur; the distal end of this tendon broadens somewhat and fuses to the
medial surface of M. gastrocnemius pars media (continuous with the
tendon of the latter); the superficial part of this tendon continues
toward the tibiotarsus, soon fusing to the deep surface of the overlying
tendon of M. flexor cruris medialis; thus the common tendon of M. flexor
cruris lateralis and M. femorocruralis insert in common with both M.
flexor cruris medialis and M. gastrocnemius pars media.

INNERVATION.--A branch of the middle tibial division of the sciatic
nerve enters the substance of M. caudofemoralis pars iliofemoralis, and
emerges near its ventral edge, then passes lateral to M. caudofemoralis
pars caudifemoralis and enters the anterior part of M. flexor cruris
lateralis.

INDIVIDUAL VARIATION.--In three legs, the nerve does not perforate M.
caudofemoralis pars iliofemoralis, but passes deep to it.

_T. cupido_

INDIVIDUAL VARIATION.--In one leg, a small accessory slip arises from
the ventrolateral surface of the caudal musculature and joins the
posterior edge of the main part of M. flexor cruris lateralis a short
distance dorsal to the pubis. In several legs, the nerve does not
perforate M. caudofemoralis pars iliofemoralis, but passes deep to it.

_P. p. jamesi_

DIFFERENCES FROM TYPICAL _T. pallidicinctus_.--The muscle is wider. The
extreme proximal end is fleshy up to its origin, which is fleshy and
tendinous from the vertebrae. The common insertional tendon of M. flexor
cruris lateralis and M. femorocruralis fuses with the distal end of the
fleshy part (instead of tendon) of M. flexor cruris medialis.

INDIVIDUAL VARIATION.--None of significance.


=_M. Flexor Cruris Medialis_= (M. semimembranosus), Figs. 12, 13, 14,
15, 16, 17, 20E

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Most posterior muscle on medial
surface of thigh; long and strap-shaped; bounded anteriorly by M.
adductor profundus; posteroproximal corner of latter medial to
anteroproximal part of M. flexor cruris medialis; bounded laterally by
Mm. caudofemoralis (proximally) and flexor cruris lateralis (distally);
anteroproximal corner adjacent to posteroventral corner of M. flexor
ischiofemoralis and lateral to extreme posteroproximal corner of M.
adductor superficialis; distal end tendinous, extending into proximal
part of shank; bounded medially by M. gastrocnemius pars interna and
laterally by Mm. gastrocnemius pars media and plantaris.

ORIGIN.--The muscle arises by a wide flat tendon from a narrow line on
the lateral surface of the ischium dorsal to the ventral ischiatic
tubercle.

INSERTION.--The wide flat tendon attaches to a narrow line on the medial
surface of the proximal part of the tibiotarsus a short distance
anterior to the proximal part of M. plantaris and deep to M.
gastrocnemius pars interna; the proximal end attaches immediately
anterior to the distal end of the medial collateral ligament. Part of
the common tendon of Mm. flexor cruris lateralis and femorocruralis
fuses with the lateral surface of the tendon of M. flexor cruris
medialis, inserting in common with it.

INNERVATION.--A branch of the middle tibial division of the sciatic
nerve passes deep to both heads of M. caudofemoralis and enters the
anterior part of M. flexor cruris medialis.

INDIVIDUAL VARIATION.--In several legs, the anterior edge of the
proximal part fits into a deep longitudinal groove in the posterior edge
of the proximal part of M. adductor superficialis; the two muscles fuse
slightly at this point.

_T. cupido_

INDIVIDUAL VARIATION.--In two legs, the extreme posterior end of the
origin is from the pubis. In two others, the proximal end is separated
by a slight gap from M. adductor superficialis. The nerve arises from
the posterior (rather than middle) tibial division in one leg.

_P. p. jamesi_

DIFFERENCES FROM TYPICAL _T. pallidicinctus_.--The origin is wider; the
posterior third to half of the origin is fleshy. The entire origin is
from a strongly curved line, the middle part of which attaches to the
ventral edge of the ischium posterior to the ventral ischiatic tubercle.
The insertion is wider. The insertional tendon attaches posterior
(rather than anterior) to the distal end of the medial collateral
ligament; the proximal end of the insertion attaches to the articular
capsule (fig. 20E). The insertional tendon is shorter; as a result, the
common tendon of Mm. flexor cruris lateralis and femorocruralis fuses
with the distal end of the fleshy belly (instead of the tendon) of M.
flexor cruris medialis.

INDIVIDUAL VARIATION.--In two thirds of the legs, the proximal part of
the insertion is fleshy rather than tendinous. In one leg, the middle
part of the insertional tendon splits into two sheets, one attaching
anterior to and one attaching posterior to the distal end of the medial
collateral ligament. The nerve may arise from the posterior tibial
division (two legs), from the middle tibial division (one leg), or as an
independent division of the tibial nerve (three legs). In one leg, the
nerve perforates the lateral part of M. flexor ischiofemoralis.


=_M. Caudofemoralis_= (M. piriformis), Figs. 12, 13, 14, 15, 16, 20J

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Posterior to proximal part of shaft
of femur and deep to M. extensor iliofibularis; posterior part deep to
M. flexor cruris lateralis; bounded medially by Mm. flexor
ischiofemoralis (dorsally), flexor cruris medialis (posteriorly), and
adductor superficialis (anteroventrally); anterior end distal to
anterior end of M. flexor ischiofemoralis; two distinct heads--pars
iliofemoralis and pars caudifemoralis; _pars iliofemoralis_ dorsal to
pars caudifemoralis; posteroventral corner of former overlapped by
latter; pars iliofemoralis wider and much shorter than pars
caudifemoralis; extreme posterior end of pars iliofemoralis fused to
overlying posteroproximal aponeurosis of M. extensor iliotibialis
lateralis; small part of ventral edge sometimes fused with underlying
tendinous posteroproximal corner of M. flexor cruris medialis; entirely
fleshy except for small triangular tendinous area along dorsal margin at
point where branch of middle tibial division of sciatic nerve passes
deep to muscle; _pars caudifemoralis_ long, thin, narrow, and
strap-shaped; overlapping posteroventral corner of ischium; posterior
end of fleshy belly narrowed and forming long slender tendon passing
into caudal musculature; anterior end forming short narrow tendon fused
to deep surface of ventral edge of pars iliofemoralis relatively near
insertion; tendon continuous to insertion; fleshy anterodorsal corner of
pars caudifemoralis slightly overlapped by ventral edge of pars
iliofemoralis; some form of connection usually present between anterior
part of M. caudofemoralis pars caudifemoralis and dorsal end of raphe
between Mm. flexor cruris lateralis and femorocruralis, most often
consisting of narrow weak tendon.

ORIGIN.--_Pars iliofemoralis_: This arises fleshily from the
ventromedial surface of the posterior part of the lateral iliac process,
from the entire lateral ischiatic ridge, and from the lateral surface of
the ischium anterior to this ridge nearly as far forward as the
posterior edge of origin of M. flexor ischiofemoralis; the
posteroventral corner reaches the ventral edge of the ischium and
usually attaches to the ischiopubic membrane posterior to M. flexor
cruris medialis. _Pars caudifemoralis_: This arises by a narrow tendon
from the ventral surface of a broad, thick, tendinous sheet ventral to
the pygostyle, which, in turn, attaches to the ventral surface of the
pygostyle.

INSERTION.--The common belly formed by the union of the two heads
narrows (width variable) and attaches to the posterolateral surface of
the femur distal to the level of insertion of M. iliacus and in contact
with the posterior edge of origin of M. vastus lateralis pars lateralis;
the dorsal part is fleshy and the ventral part is tendinous.

INNERVATION.--A branch of the middle tibial division of the sciatic
nerve gives several twigs to the deep surface of pars iliofemoralis;
another twig enters the substance of pars iliofemoralis and emerges from
the ventral edge of the latter, then enters the dorsal edge of pars
caudifemoralis. The latter twig was not found in all legs, but was
probably destroyed during dissection.

INDIVIDUAL VARIATION.--The tendinous area in the dorsal margin of pars
iliofemoralis is lacking in one leg and extremely small in some others.
In both legs of one specimen, the connection between M. caudofemoralis
pars caudifemoralis and the raphe between Mm. flexor cruris lateralis
and femorocruralis consists of a small (11 × 2 mm.) but well developed
and entirely fleshy muscle slip (fig. 16). In one leg, the ventral third
of this connection is fleshy, the remainder tendinous; in another, this
connection is completely lacking.

_T. cupido_

INDIVIDUAL VARIATION.--The tendinous area in the dorsal margin of pars
iliofemoralis is lacking in one leg. The connection between pars
caudifemoralis and the raphe between Mm. flexor cruris lateralis and
femorocruralis is lacking in several legs. A conspicuous variation
occurring in three legs is the presence of a tendinous area in the belly
of pars caudifemoralis, dividing the latter into proximal and distal
parts (fig. 20J). In one leg, the posteroventral corner of pars
iliofemoralis arises from the pubis. The origin of pars caudifemoralis
in three legs is directly from the anteroventral surface of the
pygostyle. In one instance, the insertional tendon of pars
caudifemoralis is long and extremely slender and extends for some
distance in a groove on the medial surface of pars iliofemoralis before
fusing with the latter.

_P. p. jamesi_

DIFFERENCES FROM TYPICAL _T. pallidicinctus_.--There is no connection at
all between pars caudifemoralis and the raphe between Mm. flexor cruris
lateralis and femorocruralis. The posteroventral corner of pars
iliofemoralis is some distance dorsal to the ventral edge of the ischium
and, therefore, does not attach to the ischiopubic membrane.

INDIVIDUAL VARIATION.--The insertion (narrow) is entirely tendinous in
one leg.


=_M. Flexor Ischiofemoralis_= (M. ischiofemoralis), Figs. 16, 17

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Thick; on lateral surface of
anterior part of ischium; posterior end in lateral iliac fossa; deep to
Mm. extensor iliofibularis and caudofemoralis pars iliofemoralis;
overlapping ventral extrapelvic part of M. obturator and anteroproximal
part of M. adductor superficialis (slightly fused to proximal edge of
latter); posteroventral corner contacting anteroproximal corner of M.
flexor cruris medialis; extreme anterodorsal corner usually overlapped
by tendon of M. piriformis.

ORIGIN.--The muscle arises fleshily from a large area on the lateral
surface of the ischium extending ventrally to the origin of M. adductor
superficialis, anteriorly to the level of the posterior end of the
obturator foramen, dorsally to the ventral border of the ilio-ischiatic
fenestra and to the depth of the lateral iliac fossa, and posteriorly
approximately to the level of the ventral ischiatic tubercle.

INSERTION.--The short flat tendon attaches to the lateral surface of the
femur immediately posterior to the insertion of M. piriformis.

INNERVATION.--The posterior tibial division of the sciatic nerve
penetrates the dorsal surface.

INDIVIDUAL VARIATION.--The ventral part of the insertion may be fleshy.

_T. cupido_

INDIVIDUAL VARIATION.--None of significance.

_P. p. jamesi_

INDIVIDUAL VARIATION.--In all the legs except one, an additional twig
arises from the branch to M. flexor cruris medialis and penetrates the
lateral surface of M. flexor ischiofemoralis. The ventral part of the
insertion is fleshy in one leg.


=_M. Adductor Superficialis_= (M. adductor longus et brevis, pars
externa), Figs. 14, 16, 17

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Posterior to femur, lateral to M.
adductor profundus, and medial to Mm. flexor ischiofemoralis,
caudofemoralis, and femorocruralis; proximal end (fleshy) fused to
proximal tendinous end of M. adductor profundus.

ORIGIN.--The origin is fleshy and tendinous from the proximal end of the
lateral surface of M. adductor profundus and from a narrow line on the
ischium adjacent (dorsal) to the origin of the latter; the posterior
part of the origin sometimes extends farther dorsally on the lateral
surface of the ischium; the origin does not extend so far anteriorly nor
so far posteriorly as the origin of M. adductor profundus; the anterior
edge is at the posterior border of the obturator foramen.

INSERTION.--The attachment is fleshy and thick (distal end thin) to the
posterior surface of the middle part of the femur between the posterior
and posterolateral intermuscular lines; the attachment is adjacent
(lateral) to the insertion of M. adductor profundus and adjacent
(medial) to the origins of Mm. vastus lateralis (proximally) and
femorocruralis (distally); the proximal edge is approximately at the
level of the distal edge of the insertion of M. caudofemoralis.

INNERVATION.--A branch of the obturator nerve emerges from the obturator
foramen dorsal to the tendon of insertion of M. obturator pars postica,
turns ventrally (crossing latter), and passes deep to the anteroproximal
corner of M. adductor superficialis, extending posterodistally between
the adductor muscles and giving twigs to the medial surface of M.
adductor superficialis and to the lateral surface of M. adductor
profundus.

INDIVIDUAL VARIATION.--The anterior edges of the two adductor muscles
are so firmly fused together in some cases that the boundaries cannot be
identified at this point. In several legs, there is a deep longitudinal
groove in the posterior edge of the proximal part of the muscle into
which the anterior edge of M. flexor cruris medialis fits.

_T. cupido_

INDIVIDUAL VARIATION.--In some cases, the anterior edges of the two
adductor muscles are firmly fused together.

_P. p. jamesi_

DIFFERENCES FROM TYPICAL T. PALLIDICINCTUS.--The origin is narrower.

INDIVIDUAL VARIATION.--The anterior edges of the two adductor muscles
may be fused together. In one leg, the entire muscle is
indistinguishably fused with M. adductor profundus and they appear as a
single muscle.


=_M. Adductor Profundus_= (M. adductor longus et brevis, pars interna),
Figs. 13, 15, 17, 18

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Broad; on medial surface of thigh
immediately posterior to femur; bounded posteriorly by M. flexor cruris
medialis (medial to anteroproximal corner of latter), anteriorly by M.
femoritibialis internus (anterior edge overlapped by latter), and
laterally by Mm. adductor superficialis and femorocruralis; proximal end
tendinous (except anterior edge), fused to proximal fleshy end of M.
adductor superficialis.

ORIGIN.--The muscle arises tendinously from the ventral edge of the
ischium extending from the posterior border of the obturator foramen to
the ventral ischiatic tubercle and (anterior edge) fleshily from the
lateral surface of the pubis ventral to the obturator foramen; the
origin is adjacent (ventral) to the origin of M. adductor
superficialis.

INSERTION.--The attachment is fleshy and tendinous from the posterior
intermuscular line and (proximally and distally) from a narrow adjacent
area. Proximally there are often two approximately parallel lines a
short distance apart, representing points of attachment of the lateral
and medial edges of the muscle; if there is only one line proximally, it
may represent the attachment of either the lateral or medial edge of the
muscle; distally there is usually only one line, representing the
lateral edge of the muscle. The distal end extends onto the posterior
surface of the proximal part of the internal condyle, and is adjacent
(lateral) to the origin of M. femoritibialis internus, adjacent (medial)
to Mm. adductor superficialis and femorocruralis, and adjacent
(proximal) to M. gastrocnemius pars media.

INNERVATION.--See M. adductor superficialis.

INDIVIDUAL VARIATION.--The anterior edges of the two adductor muscles
are strongly fused together in some cases.

_T. cupido_

INDIVIDUAL VARIATION.--The anterior edge may be fused with that of M.
adductor superficialis. The distal end is sometimes slightly fused with
M. gastrocnemius pars media. In one leg, the proximal two thirds of the
insertion is entirely tendinous, whereas in another the distal end of
the insertion is tendinous.

_P. p. jamesi_

INDIVIDUAL VARIATION.--The anterior edge (in one leg the entire muscle)
in some legs fuses with that of M. adductor superficialis.


=_M. Obturator_= (M. obturator externus + M. obturator internus), Figs.
16, 17, 18, 19C, D, 20K, L, M

I am adopting the single name M. obturator for the complex that Fisher
(Fisher, 1946; Fisher and Goodman, 1955) subdivides into Mm. obturator
externus and obturator internus. The reasons for this change are given
in the section on terminology.

For ease of description, it is desirable to apply names to the
subdivisions of M. obturator. It has been customary to divide the
obturator complex into two parts--an obturator internus and an obturator
externus; the latter has often been further subdivided. The evidence
given below demonstrates that a primary division of the complex into
only two parts is unsatisfactory.

I strongly suspect that comparable parts of the obturator complex have
been considered a part of the "internus" in some birds and a part of the
"externus" in others. In their work on the Galliformes, Hudson, _et al._
(1959) subdivide the obturator complex into only two
divisions--obturator externus and obturator internus. The extrapelvic
part of this complex that arises from the rim of the obturator foramen
and inserts in common with the stout tendon of the main intrapelvic part
of the obturator internus is considered by them to be a part of the
obturator internus. Their obturator externus lies anterior and deep to
the extrapelvic part of the obturator internus and inserts separately
from the latter. (I also have found this same arrangement in
_Tympanuchus_ and _Pedioecetes_.)

Berger (1952), in his description of the Black-billed Cuckoo (_Coccyzus
erythrophthalmus_), also divides the obturator complex into an obturator
internus and an obturator externus; the latter he subdivides into a
dorsal and a ventral part. He states (p. 530) that he did not find any
measurable differences in myology between _C. erythrophthalmus_ and _C.
americanus_. In order better to compare this arrangement with that in
_Tympanuchus_, I have examined two specimens of _C. americanus_. My
findings in the latter differ from Berger's description (p. 541) in one
respect. Whereas Berger states that the dorsal and ventral parts of M.
obturator externus are distinct except at their origin, I find them
fused for their entire length; the muscle fibers that connect these two
parts lie deep to the tendon of M. obturator internus. The origin of all
parts of the complex in _Coccyzus_ is similar to that in _Tympanuchus_.
The only notable difference in configuration is that the part in
_Coccyzus_ that appears to correspond to the obturator externus of
Hudson, _et al._ (1959) is not separate from the remainder of the
extrapelvic part of the muscle. Berger (1952) considers all parts of the
muscle having an extrapelvic origin to make up the obturator externus.
It appears to me that the dorsal part and a part of the ventral part of
the obturator externus of Berger correspond to the extrapelvic fleshy
part of the obturator internus of Hudson, _et al._

From my limited study, it seems to me to be desirable to recognize four
subdivisions of the obturator complex, for which I propose the terms
pars antica, pars dorsalis, pars ventralis, and pars postica. These
parts exhibit various degrees of fusion in different groups of birds and
some parts appear to be absent in certain birds. A study of a wide
variety of birds will be required to determine whether or not a
subdivision into the four parts proposed here is suitable for birds as a
whole.

Applying these terms to _Coccyzus_, pars postica is equivalent to the
entire obturator internus of Berger (1952). Pars dorsalis is apparently
equivalent to the dorsal part of Berger's obturator externus. The
ventral part of the obturator externus of Berger represents the fused
pars antica and pars ventralis.

The main parts of the obturator muscle appear to be pars postica and
pars antica. Pars dorsalis and pars ventralis are more variable; in
_Coccyzus_ these two parts are closely associated with pars antica
whereas in _Tympanuchus_ they are most closely associated with pars
postica. Apparently pars dorsalis and pars ventralis may be absent in
some birds.

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Deeply situated immediately
posterior to head of femur; part extending through obturator foramen and
lying inside pelvis; extrapelvic part deep to Mm. flexor ischiofemoralis
and piriformis; muscle partially divisible into four parts--pars antica,
pars dorsalis, pars ventralis, and pars postica (fig. 20K); _pars
postica_: mostly inside pelvis; much larger than other parts; broad
(narrow anteriorly); on medial surface of ischium; composed of several
fascicles; anterior end forming narrow, heavy tendon (with some fleshy
fibers on posterior part of deep surface) passing through obturator
foramen; anteriormost fleshy fibers of ventralmost fascicle fused with
pars ventralis; _pars ventralis_: essentially extrapelvic (see origin);
mostly ventral to tendon of pars postica; superficial to pars antica;
fused to anterior fleshy part of pars postica; anterodorsal edge usually
adjacent to, and often slightly fused with, ventral edge of pars
dorsalis (deep to tendon of pars postica); _pars dorsalis_: entirely
extrapelvic; mostly dorsal to tendon of pars postica; superficial to
dorsal part of pars antica; _pars antica_: extremely short but
relatively thick; entirely fleshy; entirely extrapelvic; between
obturator foramen and head of femur; anterior surface adjacent to
articular capsule; almost completely covered by other parts of muscle;
proximal end of posterior surface often slightly fused with adjacent
parts of pars ventralis and pars dorsalis.

ORIGIN.--_Pars postica_: This arises fleshily from the medial surface of
the entire ischium except the posterior end, from the dorsomedial and
medial surfaces of the anterior half of the pubis as far forward as the
obturator foramen, from the internal ilio-ischiatic crest, from the
medial surface of the ilium for a short distance posterior to this
crest, and from the iliac recess; the posteroventral corner usually
arises from the medial surface of the ischiopubic membrane. _Pars
ventralis_: This arises fleshily from the dorsomedial edge of the
ventral border of the obturator foramen (fig. 20M) and (narrowly) from
the anterior border of the foramen; this part may or may not arise from
the lateral surface of the anteroventral border of the foramen and is
usually adjacent along the anterior border of the foramen to pars
dorsalis; _pars ventralis_ is continuous along the ventral border of the
foramen with the intrapelvic origin of pars postica. _Pars dorsalis_:
This arises fleshily from the lateral surface of the anterodorsal border
of the foramen (fig. 20L) and may extend posteriorly along the dorsal
border of the foramen. _Pars antica_: This arises fleshily from the
depresssed area anterior to the obturator foramen (adjacent to pars
dorsalis and pars ventralis); the posteroventral corner may arise from
the lateral surface of the anteroventral border of the obturator foramen
(ventral to the anterior end of pars ventralis; fig. 20L).

INSERTION.--_Pars postica_: Several tendinous bands (intrapelvic)
converge and coalesce, forming a single strong tendon that passes
through the obturator foramen and attaches to the lateral surface of the
femoral trochanter a short distance posterior to the insertion of M.
gluteus profundus and proximal to the insertion of M. flexor
ischiofemoralis. _Pars ventralis_: The attachment is fleshy and
tendinous to the ventral edge and the deep surface of the tendon of pars
postica. _Pars dorsalis_: The attachment is fleshy and tendinous to the
dorsal edge of the tendon of pars postica. _Pars antica_: The attachment
is fleshy to the posterior surface of the proximal end of the femur
several mm. posterior to the insertion of pars postica; the lateral edge
attaches to the obturator ridge.

INNERVATION.--The muscle is supplied by the obturator nerve; several
twigs, which do not pass through the obturator foramen, penetrate the
anterior part of the medial surface of pars postica; several twigs pass
through the obturator foramen and supply pars dorsalis, pars ventralis,
and pars antica.

INDIVIDUAL VARIATION.--In some cases the origin of pars postica does not
include the dorsal end of the internal ilio-ischiatic crest nor the
ilium posterior to it. Tiny but distinct accessory slips are sometimes
present. In one leg a tendinous slip of pars antica extends beyond the
remainder of the muscle and inserts independently on the trochanter
close to the insertion of pars postica. In another leg, a fleshy and
tendinous slip of pars antica attaches to the deep surface of the
insertional tendon of pars postica. In still another leg, a fleshy and
tendinous slip of pars dorsalis inserts adjacent (anterior) to the
dorsal edge of the insertion of pars antica.

_T. cupido_

INDIVIDUAL VARIATION.--The variations are similar to those given above
for _T. pallidicinctus_ except that there is no slip of pars antica
attaching to the tendon of pars postica.

_P. p. jamesi._

INDIVIDUAL VARIATION.--There are variations similar to those given above
for _T. pallidicinctus_ except that there is no independent slip of pars
antica attaching on the trochanter close to the insertion of pars
postica. Pars dorsalis may be quite small. In several legs, pars
dorsalis is more closely associated with pars antica than with pars
postica; in one of these, pars dorsalis is indistinguishably fused with
pars antica (inserting with the latter) except for a few fibers which
insert with pars postica.


=_M. Femorocruralis_= (M. accessorius semitendinosi), Figs. 14, 15, 16,
17

Fisher (Fisher, 1946; Fisher and Goodman, 1955) considers this muscle as
an accessory head of M. flexor cruris lateralis. The reasons for this
change in terminology are given in the section on terminology.

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Short and broad; posterior to distal
part of femur; deep to Mm. extensor iliofibularis and vastus lateralis
pars postica; bounded posteriorly by M. flexor cruris lateralis,
medially by Mm. adductor superficialis and adductor profundus, and
distally by M. gastrocnemius pars media; fused to a variable degree with
the latter (in some cases these two muscles fused firmly together,
appearing as single muscle); distal and medial to proximal end of M.
flexor perforatus digiti IV.

ORIGIN.--The muscle arises fleshily (thin proximally, thick distally)
from the posterior surface of approximately the distal half of the femur
between the posterior and posterolateral intermuscular lines. The
ventral end is continuous with the origin of M. gastrocnemius pars
media, adjacent (medial) to the origin of M. vastus lateralis pars
postica, and adjacent (lateral) to the insertions of Mm. adductor
superficialis and adductor profundus.

INSERTION.--The attachment is to the tendinous raphe in common with M.
flexor cruris lateralis (which see).

INNERVATION.--One or two tiny branches come off the tibial nerve near
the distal end of the main trunk of the sciatic nerve, pass anteriorly
deep to the peroneal nerve, and penetrate the lateral surface.

INDIVIDUAL VARIATION.--In two legs, the branch of the medial division of
the tibial nerve which supplies M. gastrocnemius pars media sends a twig
to the lateral surface of the distal end of M. femorocruralis (in
addition to the usual innervation).

_T. cupido_

INDIVIDUAL VARIATION.--None of significance.

_P. p. jamesi_

DIFFERENCES FROM TYPICAL _T. pallidicinctus_.--The muscle is much wider,
extending farther proximally on the femur.

INDIVIDUAL VARIATION.--None of significance.


=_M. Gastrocnemius_=, Figs. 12, 13, 15

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Divided into three distinct, widely
separated parts--pars externa, pars interna, and pars media; _pars
externa_: large; on posterolateral surface of shank; narrow proximally
and distally; bounded anterolaterally by M. flexor perforans et
perforatus digiti II and anteromedially by medial head of M. flexor
perforatus digiti III; completely separate from pars interna and media
except for common tendon of insertion; _pars interna_: large; on
anteromedial surface of shank; narrow distally; bounded anterolaterally
by M. peroneus longus and posteromedially by pars media (proximally) and
medial head of M. flexor perforatus digiti III; broad sheet of tough
connective tissue extending between distal parts of pars externa and
pars interna; covering underlying M. flexor perforatus digiti III
(medial head), somewhat fused with anteroproximal edge of M. peroneus
longus; _pars media_: small and short; on medial surface of proximal
part of shank; deep to tendon of insertion of M. flexor cruris medialis;
bounded anteromedially by pars interna, posterolaterally by medial head
of M. flexor perforatus digiti III, and proximally by M. femorocruralis;
fused to latter, and boundary between the two difficult to locate.

ORIGIN.--_Pars externa_: The short cylindrical tendon fuses with the
anterior half of the distal arm of the tendinous guide loop for M.
extensor iliofibularis and attaches in common with the latter to the
posterolateral surface of the femur immediately proximal to the fibular
condyle; the attachment is proximal (adjacent) to the origin of M.
flexor perforans et perforatus digiti II and distal (adjacent) to the
origin of M. flexor perforatus digiti IV and is fused to the articular
capsule.

_Pars interna_: The proximal end is partly separable into two layers--a
superficial longer one and a deep shorter one. The superficial layer
attaches fleshily to the ventral part of the anterior surface of the
patella and to the medial half of the superficial surface of the
patellar tendon; this layer slightly overlaps the distal fleshy end of
M. extensor iliotibialis anticus. The deep layer (overlapped by the
superficial layer) attaches to the medial surface of the inner cnemial
crest, to the rotular crest medial to the latter, to the medial surface
of the proximal part of the tibiotarsus, and (posteroproximal corner) to
the distomedial edge of the patellar tendon and to the articular capsule
posteromedial to the rotular crest; the entire ventral edge is
tendinous, the remainder fleshy.

_Pars media_: This arises fleshily from an oblique line beginning at the
distal end of the origin of M. femorocruralis (continuous with the
latter) and extending distomedially across the proximal part of the
popliteal area to the proximal edge of the internal condyle, then
attaching to the adjacent part of the articular capsule; this part is
adjacent (distal) to the insertion of M. adductor profundus and adjacent
(proximomedial) to the medial head of M. flexor perforatus digiti IV.

INSERTION.--_Pars media_ narrows distally with a narrow tendon along the
posterior edge of the fleshy belly; approximately one third of the way
down the tibiotarsus the fleshy part terminates and the tendon joins the
posterior edge of pars interna, continuing distally in this position.
The ossified tendon on the superficial surface of the distal part of
_pars interna_, continuous posteriorly with the tendon of pars media, is
joined approximately two thirds of the way down the tibiotarsus by the
tendon of pars externa; the fleshy belly of pars interna ends just below
the junction. The ossified tendon on the superficial surface of the
distal part of _pars externa_ extends beyond the fleshy belly and
becomes flexible before joining the tendon of pars interna and media.
The common tendon (partly ossified) extends along the posterior surface
of the tibiotarsus and widens as it passes posterior to the tibial
cartilage, bound to the latter by a thin tough sheet of connective
tissue which attaches to the edges of the tibial cartilage, thus forming
a sheath for the tendon; the tendon attaches by its edges to the
posterior edges of the calcaneal ridges of the hypotarsus, then
continues distally (much reduced in thickness) along the posterior
surface of the tarsometatarsus, enclosing the flexor tendons; the
lateral edge of the tendon attaches to the posterolateral edge of the
tarsometatarsus, terminating immediately above the level of the hallux;
the medial edge attaches to the edge of the posterior metatarsal crest;
the tendon terminates as a thin sheet that attaches to the fascia on the
sole of the foot. (Hudson, _et al._, 1959 consider the posterior
metatarsal crest to be an ossified part of the tendon of M.
gastrocnemius.)

INNERVATION.--A branch of the lateral division of the tibial nerve
penetrates the proximal part of the medial surface of pars externa. One
or two branches of the medial division of the tibial nerve pass deep to
M. plantaris and penetrate the deep surface of the posterior part of
pars interna. The most proximal branch of the medial division of the
tibial nerve penetrates the lateral surface of pars media.

INDIVIDUAL VARIATION.--None of significance.

_T. cupido_

INDIVIDUAL VARIATION.--In one leg, the lateral edge of pars interna
overlaps the proximomedial edge of M. peroneus longus; some fibers
attach to the lateral surface of the inner cnemial crest.

_P. p. jamesi_

DIFFERENCES FROM TYPICAL _T. pallidicinctus_.--The proximal end of pars
interna does not reach the patella.

INDIVIDUAL VARIATION.--In one leg, an additional twig to pars media
arises from the distal branch to M. femorocruralis.


=_M. Flexor Perforans et Perforatus Digiti II_=, Figs. 12, 14

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Long, slender, and Y-shaped; on
lateral surface of shank; the two heads enclosing M. flexor perforans et
perforatus digiti III; _posterior head_ bounded posteriorly by M.
gastrocnemius pars externa; extreme proximal end deep to M. vastus
lateralis pars postica; anterior surface fused to posterior surface of
M. flexor perforans et perforatus digiti III; deep surface fused to
tendinous part of lateral head of M. flexor perforatus digiti IV;
_anterior head_ tendinous except for extreme distal end; covered by, and
fused to, posterior edge of M. peroneus longus; fused to anterior
surface of M. flexor perforans et perforatus digiti III; two heads join
above middle of shank; anteroproximal and posterodistal parts of common
belly usually tendinous.

ORIGIN.--_Anterior head_: This arises by a narrow tendon (partly
ossified) from the distal tip of the outer cnemial crest. The tendon is
so intimately fused with a connective tissue sheet fused to the deep and
posterior surfaces of M. peroneus longus and to the anterior surface of
M. flexor perforans et perforatus digiti III that M. flexor perforans et
perforatus digiti II could be considered to arise from these two
muscles. _Posterior head_: This arises mostly fleshily from the lateral
surface of a compound sheet of tough connective tissue formed by the
fusion of the tendinous posteroproximal corner of M. flexor perforans et
perforatus digiti III, the proximal parts of the tendons of origin of
the lateral heads of Mm. flexor perforatus digiti IV and flexor
perforatus digiti II, the fibular and distal arms of the guide loop for
M. extensor iliofibularis, and the lateral part of the articular
capsule; a part of the common tendon of origin of the anterolateral
heads of Mm. flexor perforatus digiti III, flexor perforatus digiti IV,
and flexor perforatus digiti II also contributes to this sheet, which
attaches to the lateral surface of the external condyle of the femur and
to the anterolateral surface of the head of the fibula; for convenience
in description, this complex connective tissue sheet will hereafter be
termed the _femorofibular fascia_. The anteroproximal corner of the
posterior head of M. flexor perforans et perforatus digiti II often
attaches to the lateral surface of the vinculum that passes from the
femorofibular fascia to the deep surface of the patellar tendon; the
extreme proximal end usually attaches fleshily to a small area on the
femur immediately proximal to the fibular condyle and adjacent (distal)
to the attachment of the distal arm of the guide loop for M. extensor
iliofibularis.

INSERTION.--The common belly terminates approximately two thirds of the
way down the shank; the slender ossified tendon begins along the
posteromedial edge of the common belly, continues distally along the
posterior surface of the shank, and becomes flexible before passing
through the canal in the tibial cartilage that lies posteromedial to the
canal for M. flexor digitorum longus. The tendon passes with the tendon
of M. flexor perforatus digiti II (medial to the latter) through a canal
in the hypotarsus (see M. flexor perforatus digiti II); just below the
hypotarsus, the tendon becomes superficial to the tendon of M. flexor
perforatus digiti II and farther distally becomes lateral and finally
deep to the latter; the tendon is ossified for most of the length of the
tarsometatarsus. At the distal end of this bone, the tendon expands
before passing onto the ventral surface of digit II between the tendons
of Mm. flexor perforatus digiti II and flexor digitorum longus; at the
level of the first phalanx, the edges of the tendon extend dorsally
around the tendon of M. flexor digitorum longus and fuse, forming a
sheath around the latter; the latter emerges from the sheath near the
distal end of the first phalanx; the tendon attaches to the proximal end
of the subarticular cartilage ventral to the first interphalangeal joint
(the strongest attachment is on the medial side).

INNERVATION.--The lateral division of the tibial nerve sends twigs into
the posteromedial edge of the posterior head.

INDIVIDUAL VARIATION.--In one leg, the fleshy part of the anterior head
is unusually long. In another leg, the anterior head is entirely
tendinous. In one leg, a bundle of fibers of the posterior head attaches
to the deep surface of the distal part of the patellar tendon. In one
leg, near the middle of the tarsometatarsus a rather long and narrow but
thick and strong vinculum arises from the tendon of M. flexor perforatus
digiti II and, farther distally, joins the tendon of M. flexor perforans
et perforatus digiti II.

_T. cupido_

INDIVIDUAL VARIATION.--In one leg, the posterior head arises in part
from the distolateral edge of the patellar tendon and in another, in
part from the superficial surface of the distolateral corner of the
patellar tendon.

_P. p. jamesi_

INDIVIDUAL VARIATION.--None of significance.


=_M. Flexor Perforans et Perforatus Digiti III_=, Figs. 12, 14

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Thick, bipinnate; on lateral surface
of proximal part of shank between two heads of M. flexor perforans et
perforatus digiti II; bounded anteriorly by M. peroneus longus; anterior
surface fused with tendinous anterior head of M. flexor perforans et
perforatus digiti II; anterolateral edge somewhat fused to posterior
edge of M. peroneus longus superficial to latter tendon; posterior
surface fused to posterior head of M. flexor perforans et perforatus
digiti II; distal part of belly covered by common belly of latter
muscle; posteromedial edge fused to underlying lateral head of M. flexor
perforatus digiti IV; anteromedial edge usually somewhat fused to
underlying M. flexor digitorum longus.

ORIGIN.--The origin is fleshy and tendinous from the edge of the outer
cnemial crest and fleshy from the superficial surface of the
distolateral part of the patellar tendon; the posteroproximal corner
arises tendinously from the femorofibular fascia.

INSERTION.--The belly narrows abruptly, terminating approximately at the
middle of the shank; the slender ossified tendon extends posterodistally
along the shank, becoming flexible before passing posterior to the
tibial cartilage deep to the tendon of M. gastrocnemius, medial to the
tendon of M. flexor perforatus digiti IV, and superficial to the medial
half of the tendon of M. flexor perforatus digiti III; a thin sheet of
connective tissue covers the tendon and attaches by its edges to the
underlying tendon of M. flexor perforatus digiti III (thus the latter
tendon forms a sheath for the tendon of M. flexor perforans et
perforatus digiti II); the tendon is ossified for most of the length of
the tarsometatarsus; at midlength of the latter, the tendon lies between
the tendons of Mm. flexor perforatus digiti IV and flexor perforatus
digiti III; near the distal end of the tarsometatarsus, the tendon
becomes lateral and then deep to the tendon of M. flexor perforatus
digiti III and is connected by a vinculum to the latter (which see). The
tendon enters the ventral surface of digiti III between the tendons of
Mm. flexor perforatus digiti III and flexor digitorum longus; after
sending a dorsal slip (lateral to the tendon of M. flexor digitorum
longus) to the subarticular cartilage ventral to the first
interphalangeal joint, the tendon divides into two branches, between
which emerges the tendon of M. flexor digitorum longus; the lateral
branch attaches to the subarticular cartilage of the second
interphalangeal joint and to the lateral surface of the distal end of
the second phalanx; the medial branch has similar attachments on the
medial side of the digit.

INNERVATION.--A branch of the lateral division of the tibial nerve
passes deep to the posterior head of M. flexor perforans et perforatus
digiti II and enters the posteromedial edge of M. flexor perforans et
perforatus digiti III.

INDIVIDUAL VARIATION.--In both legs of one specimen, the part arising
from the femorofibular fascia appears as a distinct but short accessory
head. There is no significant individual variation in _T. cupido_ or _P.
p. jamesi_.


=_M. Flexor Perforatus Digiti IV_=, Figs. 14, 16

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--On posterolateral aspect of shank
deep to M. gastrocnemius pars externa; bounded medially by medial head
of M. flexor perforatus digiti III, anterolaterally by posterior head of
M. flexor perforans et perforatus digiti II, and anteriorly by M. flexor
digitorum longus; divided into three heads--medial (largest), lateral,
and anterolateral (smallest); tendon of insertion of M. extensor
iliofibularis passing between medial and lateral heads; proximal and
anteroproximal parts of _lateral head_ an extremely thin, flat tendon;
anterodistal part of tendon fused to lateral surface of fleshy part of
underlying lateral head of M. flexor perforatus digiti II; proximal part
of tendon fused indistinguishably to tendinous part of underlying
lateral head of M. flexor perforatus digiti II; fleshy part of
_anterolateral head_ anterodistal to lateral head; proximal part of
former a long slender tendon anterior to lateral head; anterior surface
of anterolateral head (both fleshy and tendinous parts) fused to tendon
of anterolateral head of M. flexor perforatus digiti III; deep surface
fused to underlying anterolateral head (fleshy) of M. flexor perforatus
digiti II; common tendon of anterolateral heads of M. flexor perforatus
digiti IV and M. flexor perforatus digiti III passing medial to tendon
of insertion of M. extensor iliofibularis, to peroneal nerve, and to
fibular arm of guide loop for M. extensor iliofibularis; tendon of M.
ambiens inserting on anterolateral surface of this common tendon;
_medial head_ entirely fleshy; medial surface fused to medial head of M.
flexor perforatus digiti III; deep surface fused to medial edge of
underlying medial head of M. flexor perforatus digiti II; medial and
lateral heads joined, forming bipinnate belly (pinnate structure most
evident on deep surface); anterolateral head joined to distolateral part
of belly.

ORIGIN.--The _medial head_ attaches fleshily to the proximal part of the
popliteal area proximal (adjacent) to the origin of M. flexor hallucis
longus and distolateral to the distal end of the origin of M.
femorocruralis; the attachment extends laterally onto the posterolateral
surface of the femur proximal (adjacent) to the common attachment of M.
gastrocnemius pars externa and the distal arm of the guide loop for M.
extensor iliofibularis; the medial edge of the origin is fused with part
of the tendinous origin of the medial head of M. flexor perforatus
digiti III.

The broad flat common tendon of the _lateral head_ and the lateral head
of M. flexor perforatus digiti II fuses to the superficial surface of
the fibular arm of the guide loop for M. extensor iliofibularis and
contributes to the femorofibular fascia; consequently the ultimate
origin would be the external femoral condyle and the head of the fibula.

The slender common tendon of the _anterolateral head_ and the
anterolateral heads of Mm. flexor perforatus digiti II and flexor
perforatus digiti III passes deep to the insertional tendon of M.
extensor iliofibularis and to the fibular arm of the guide loop for the
latter muscle (to which it partly fuses); the tendon attaches to a
narrow line on the head of the fibula adjacent to the attachment of the
fibular arm of the guide loop and to the deep part of the femorofibular
fascia.

INSERTION.--The slender ossified tendon becomes flexible before it
passes posterior to the tibial cartilage deep to the tendon of M.
gastrocnemius, lateral to the tendon of M. flexor perforans et
perforatus digiti III, and superficial to the lateral half of the tendon
of M. flexor perforatus digiti III; a thin sheet of connective tissue
covers the tendon and attaches by its edges to the underlying tendon of
M. flexor perforatus digiti III (thus the latter tendon forms a sheath
for the tendon of M. flexor perforatus digiti IV; this sheath is
separate from a similar sheath surrounding the tendon of M. flexor
perforans et perforatus digiti III); the tendon is again ossified where
it passes along the posterolateral surface of the tarsometatarsus
posterolateral to the tendon of M. flexor perforans et perforatus digiti
III; near the distal end of the tarsometatarsus the tendon becomes
flexible and expands greatly in width and thickness, and sends a small
slip dorsally, medial to the underlying tendons, that attaches to the
subarticular cartilage ventral to the trochlea for digit IV; sometimes
this slip is continuous with the retinaculum ventral to the tendon at
the level of the proximal end of the digit. Several more or less
distinct sheets of tough connective tissue lie ventral to all of the
flexor tendons at the level of the trochleae and the proximal end of the
digits, holding them in place. The tendon narrows as it passes onto the
ventral surface of digit IV and soon divides into three branches; the
tendon of M. flexor digitorum longus emerges between the medial and
middle branches. The lateral branch attaches to the subarticular
cartilage ventral to the first interphalangeal joint and is also bound
by connective tissue to the ventrolateral surface of the first phalanx.
A dorsal slip arises at the point of divergence of the lateral and
middle branches and attaches to the subarticular cartilage of the first
interphalangeal joint. The middle branch attaches to the subarticular
cartilage of the second joint. The medial branch, after sending dorsal
slips to each of the first two subarticular cartilages, attaches to the
subarticular cartilage of the third interphalangeal joint.

INNERVATION.--The posterior division of the tibial nerve sends a branch
into the posterior edge of the medial head, then passes between the
latter and the medial head of M. flexor perforatus digiti III; as it
extends distally it gives off twigs to the medial surface of the medial
head, to the deep surface of the lateral head, and to the deep surface
of the anterolateral head.

INDIVIDUAL VARIATION.--In one leg, an additional branch arises from the
tibial nerve at the level of origin of the posterior division and enters
the posterior surface of the medial head; a twig from this branch
anastomoses with the first twig of the posterior division to the same
head; a branch of the medial division joins the posterior division
distal to the origin of the twigs to the medial head but proximal to the
origin of the twigs to the other heads.

_T. cupido_

INDIVIDUAL VARIATION.--None of significance.

_P. p. jamesi_

INDIVIDUAL VARIATION.--In four legs, a tiny vinculum connects with the
tendon of M. flexor digitorum longus (which see).


=_M. Flexor Perforatus Digiti III_=, Figs. 13, 14, 15, 16, 17

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Divided into two widely separated
heads--medial and anterolateral--with completely separate bellies but
with common insertional tendon; small _anterolateral head_ on lateral
aspect of thigh deep to M. flexor perforans et perforatus digiti II and
posterior to M. flexor digitorum longus; fleshy part of head
distolateral to belly of M. flexor perforatus digiti IV; fleshy part
fused to lateral edge of belly of M. flexor perforatus digiti II;
proximal part of head a slender ossified tendon fused to anterior edge
of both fleshy and tendinous parts of anterolateral head of M. flexor
perforatus digiti IV and to lateral edge of anterolateral head of M.
flexor perforatus digiti II; this tendon passing deep to tendon of
insertion of M. extensor iliofibularis and to peroneal nerve; large
_medial head_ on posteromedial surface of thigh anterior to medial edge
of M. gastrocnemius pars externa, lateral to M. gastrocnemius pars
media, and medial to M. flexor perforatus digiti IV; fused to medial
surface of medial head of latter and to medial edges of Mm. flexor
perforatus digiti II and flexor hallucis longus; proximal end of head
tendinous.

ORIGIN.--The _medial head_ attaches tendinously to the medial part of
the popliteal area in common with the medial head of M. flexor
perforatus digiti II and with the medial edges of Mm. flexor perforatus
digiti IV (medial head) and flexor hallucis longus; and is also fused to
the articular capsule. The _anterolateral head_ arises in common with
the anterolateral heads of Mm. flexor perforatus digiti II and flexor
perforatus digiti IV (see account of latter).

INSERTION.--The short unossified tendon of the anterolateral head and
the longer ossified tendon of the medial head join (after the latter
becomes flexible) a short distance above the tibial cartilage, forming a
broad flat common tendon that passes posterior to the tibial cartilage
(in a shallow groove of the latter); the main part of the tendon is deep
to the tendons of Mm. flexor perforatus digiti IV and flexor perforans
et perforatus digiti III, but forms separate thin sheaths around these
two tendons at the level of the tibial cartilage. A thin sheet of
connective tissue covers these three tendons and attaches by its edges
to the tibial cartilage, forming a sheath for them. These three tendons
pass through the superficial groove in the hypotarsus deep to the tendon
of M. gastrocnemius; the tendon of M. flexor perforatus digiti III is
ossified for most of the length of the tarsometatarsus; a short distance
below the hypotarsus, the anterior branch of the tendon of M. peroneus
longus attaches broadly to the lateral edge of the tendon of M. flexor
perforatus digiti III. In the proximal part of the tarsometatarsus the
tendon is deep to the tendon of M. flexor perforans et perforatus digiti
III, but farther distally becomes medial and then superficial to the
latter and lateral to the tendon of M. flexor perforans et perforatus
digiti II; near the distal end of the tarsometatarsus a narrow but
strong vinculum extends from the lateral edge of the tendon somewhat
distally to the lateral edge of the tendon of M. flexor perforans et
perforatus digiti III. At the distal end of the tarsometatarsus the
tendon expands before entering the ventral surface of digit III where it
soon divides into two branches, between which emerge the tendons of Mm.
flexor perforans et perforatus digiti III and flexor digitorum longus;
the lateral branch attaches to the subarticular cartilage ventral to the
first interphalangeal joint and to the lateral surface of the distal end
of the first phalanx; the medial branch has similar attachments on the
medial side of the digit.

INNERVATION.--The posterior division of the tibial nerve passes between
the medial heads of M. flexor perforatus digiti III and M. flexor
perforatus digiti IV and sends a twig to the lateral surface of the
former, then passes deep to the common belly of M. flexor perforatus
digiti IV and sends a twig to the posterior surface of the anterolateral
head of M. flexor perforatus digiti III.

INDIVIDUAL VARIATION.--None of significance.

_T. cupido_

INDIVIDUAL VARIATION.--In one leg, an extra branch (immediately distal
to the branch to M. gastrocnemius pars media) of the medial division of
the tibial nerve penetrates the medial surface of the proximal end of
the medial head.

_P. p. jamesi_

INDIVIDUAL VARIATION.--None of significance.


=_M. Flexor Perforatus Digiti II_=, Figs. 15, 17

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Bipinnate; on posterior aspect of
shank deep to M. flexor perforatus digiti IV and between two heads of M.
flexor perforatus digiti III; bounded anteriorly by Mm. flexor digitorum
longus and flexor hallucis longus; proximal part divided into three
small heads--medial, lateral, and anterolateral; medial and proximal
parts of _medial head_ tendinous and extremely thin except for ossified
medial edge; proximal part of _lateral head_ tendinous and lateral to
insertional tendon of M. extensor iliofibularis; both tendinous and
fleshy parts fused to overlying tendon of M. flexor perforatus digiti
IV; narrow _anterolateral head_ fused to overlying anterolateral head of
latter muscle and (anterolateral edge) to ossified tendon of
anterolateral head of M. flexor perforatus digiti III; lateral edge of
common belly fused to latter head; medial edge of muscle fused to medial
heads of Mm. flexor perforatus digiti IV and flexor perforatus digiti
III and to M. flexor hallucis longus.

ORIGIN.--The _medial head_ attaches by a slender ossified tendon to the
medial part of the popliteal area in common with the medial head of M.
flexor perforatus digiti III and with the medial edges of Mm. flexor
perforatus digiti IV (medial head) and flexor hallucis longus; this
head is also fused to the articular capsule. The above-mentioned
ossified part of the tendon is situated at the junction of M. flexor
perforatus digiti II and M. flexor perforatus digiti III (medial head)
and could be considered to be a part of the latter rather than the
former. The flat tendon of the _lateral head_ arises in common with the
lateral head of M. flexor perforatus digiti IV (which see). The
_anterolateral head_ arises in common with the anterolateral heads of
Mm. flexor perforatus digiti IV and flexor perforatus digiti III (see
former).

INSERTION.--The short, slender, ossified tendon becomes flexible and
passes through the canal in the tibial cartilage that lies medial to the
canal for M. flexor hallucis longus and lateral to the canals for Mm.
flexor digitorum longus and flexor perforans et perforatus digiti II.
The tendon passes with the tendon of M. flexor perforans et perforatus
digiti II (lateral to latter) through the canal in the hypotarsus that
is deep to the groove for M. flexor perforatus digiti III and
superficial to the canal for M. flexor digitorum longus; the former
canal has a bony floor and sides but a fibrous roof; a fibrous partition
subdivides the proximal half of this canal, forming a separate channel
for each tendon. The tendon is ossified for most of the length of the
tarsometatarsus and is situated lateral (adjacent) to the posterior
metatarsal crest; immediately below the hypotarsus, the tendon becomes
situated deep to the tendon of M. flexor perforans et perforatus digiti
II and farther distally becomes situated medial and finally superficial
to the latter; at the distal end of the tarsometatarsus the tendon
expands greatly and its edges (thick) pass dorsally around the
underlying flexor tendons and become continuous with the subarticular
cartilage ventral to the trochlea for digit II. The tendon extends onto
the ventral surface of digit II and attaches by its edges to the
ventromedial and ventrolateral surfaces of the proximal part of the
first phalanx (the lateral edge extending farthest distally); the
tendons of Mm. flexor perforans et perforatus digiti II and flexor
digitorum longus emerge from the distal end of the tendon of M. flexor
perforatus digiti II.

INNERVATION.--The posterior division of the tibial nerve passes between
the medial heads of Mm. flexor perforatus digiti III and flexor
perforatus digiti IV and gives a twig to the superficial surface of each
of the three heads of M. flexor perforatus digiti II and sometimes gives
another twig to the superficial surface of the distal part of the common
belly.

INDIVIDUAL VARIATION.--In one leg, a vinculum connects the tendon with
that of M. flexor perforans et perforatus digiti II (which see).

_T. cupido_

INDIVIDUAL VARIATION.--The canal in the hypotarsus through which the
tendon passes has a bony (instead of fibrous) roof in one leg.

_P. p. jamesi_

INDIVIDUAL VARIATION.--The variation given above for _T. cupido_ is
found in both legs of one specimen.


=_M. Flexor Hallucis Longus_=, Figs. 15, 19A

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Elongate and tapering; on posterior
aspect of shank deep to M. flexor perforatus digiti II and to proximal
end of medial head of M. flexor perforatus digiti IV; bounded
anterolaterally by M. flexor digitorum longus and anteromedially by M.
plantaris; tendinous anteromedial surface of proximal end fused to
common tendon of origin of medial heads of Mm. flexor perforatus digiti
III and flexor perforatus digiti II; belly ending approximately halfway
down shank.

ORIGIN.--The origin is fleshy and tendinous (anteromedial surface) from
the popliteal area immediately distal to the origin of the medial head
of M. flexor perforatus digiti IV, extending laterally to the area
immediately proximal to the external femoral condyle (medial to the
origin of M. gastrocnemius pars externa); the muscle also arises from
the proximal end of the posterior part of the articular capsule.

INSERTION.--The slender ossified tendon becomes flexible and passes
through the canal in the tibial cartilage that lies lateral to the canal
for M. flexor perforatus digiti II, then passes through a slight groove
in the lateral surface of the hypotarsus and becomes ossified again;
midway of the tarsometatarsus, the tendon becomes superficial to the
tendon of M. flexor digitorum longus and is connected with the latter by
an extensive vinculum, which extends from the deep surface and lateral
edge of the tendon of M. flexor hallucis longus distally to the
superficial surface of the tendon of M. flexor digitorum longus; the
tendon continues, unossified and considerably reduced in size, distally
medial to the tendon of M. flexor digitorum longus, and passes through
the flexor groove of the first metatarsal anterolateral (adjacent) to
the tendon of M. flexor hallucis brevis, then passes deep to the
terminal expansion of the latter onto the ventral surface of the hallux;
the tendon emerges from under the end of the tendon of M. flexor
hallucis brevis and attaches to the ventral surface of the ungual
phalanx; a weak dorsal slip attaching to the ventral surface of the
distal end of the first phalanx is usually present.

INNERVATION.--A branch of the medial division of the tibial nerve passes
along the medial edge of the muscle, giving several twigs into it.

INDIVIDUAL VARIATION.--None of significance in any of the three species
studied.


=_M. Plantaris_=, Figs. 15, 19A

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Elongate and tapering; on
posteromedial surface of tibiotarsus; bounded medially by M.
gastrocnemius pars interna and tendon of M. flexor cruris medialis,
posteriorly by M. gastrocnemius pars media and medial head of M. flexor
perforatus digiti III, posterolaterally by M. flexor hallucis longus;
medial to M. flexor digitorum longus; anterolateral surface of proximal
end often slightly overlapping and fused to posterior surface of medial
end of M. popliteus; belly terminating above middle of shank.

ORIGIN.--The origin is fleshy and tendinous (distal edge only) from an
elongate area on the posteromedial surface of the proximal end of the
tibiotarsus adjacent to the insertion of M. popliteus.

INSERTION.--The long, slender, ossified tendon extends along the
posteromedial aspect of the tibiotarsus and becomes flexible just before
attaching to the proximomedial part of the tibial cartilage. The tibial
cartilage is a large, mostly cartilaginous pad fitting closely over the
posterior surface of the intratarsal joint; the distomedial corner is
ossified. This cartilage is perforated by the tendons of several flexor
muscles; the distal end of the cartilage attaches to the posteroproximal
corner of the tarsometatarsus.

INNERVATION.--A branch of the medial division of the tibial nerve
penetrates the lateral surface.

INDIVIDUAL VARIATION.--In one leg, a small bundle of fibers separates
from the proximal end of the muscle, forming a short accessory head
which attaches, separately from the remainder, to the articular capsule
posteroproximal to the main origin; a blood vessel passes between the
main and accessory heads.

_T. cupido_

INDIVIDUAL VARIATION.--In one leg, a small bundle of fibers arises from
the medial collateral ligament. In another leg, the nerve to M.
gastrocnemius pars interna passes through a gap in the origin of M.
plantaris rather than distal to its origin.

_P. p. jamesi_

INDIVIDUAL VARIATION.--The nerve branch supplying M. gastrocnemius pars
interna gives a minute twig to the deep surface of the free belly of M.
plantaris in one instance.


=_M. Flexor Digitorum Longus_=, Figs. 14, 16, 17, 19A

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Relatively broad; bipinnate; on
posterolateral surface of tibiotarsus; bounded posteromedially by M.
flexor hallucis longus, posteriorly by M. flexor perforatus digiti II
and anterolateral head of M. flexor perforatus digiti III, laterally by
Mm. flexor perforans et perforatus digiti III and flexor perforans et
perforatus digiti II, and anterolaterally by Mm. peroneus brevis and
tibialis anticus; anterior surface of lateral part of distal half of
common belly fused to M. peroneus brevis; divided into three
heads--posterior (largest), lateral, and medial; _posterior head_ on
posterior surface of head of fibula; overlapping and fused to lateral
end of M. popliteus; proximomedial corner deep to latter; _lateral head_
on lateral surface of fibula; lateral and posterior heads separated by
insertion of M. extensor iliofibularis; these two heads joined
immediately distal to insertion of latter; _medial head_ on posterior
surface of tibiotarsus; group of blood vessels and nerves passing
between medial and posterior heads; these two heads joined several mm.
distal to junction of lateral and posterior heads; deep surface of
insertional tendon near distal end of tarsometatarsus serving as origin
for M. lumbricalis.

ORIGIN.--_Posterior head_: This arises fleshily from the posterior
surface of the fibula beginning almost at the proximal end and from the
medial surface of the fibula beginning deep to the distal part of M.
popliteus. _Lateral head_: This arises fleshily (sometimes partly
tendinously) from the lateral surface of the fibula proximal to the
fibular tubercle. Some fibers arise from the distal edge of the tendon
of insertion of M. extensor iliofibularis. _Medial head_: This arises
fleshily from the posterior surface of the tibiotarsus just medial to
the distal part of the posterior head, distal to M. popliteus, and
either lateral or distolateral to the origin of M. plantaris. Distal to
the junction of the three heads, the muscle arises fleshily from the
posterior surface of the tibiotarsus (except the distal part) and from
the medial and posterior surfaces of the fibula.

INSERTION.--The slender ossified tendon becomes flexible and passes
through the canal in the tibial cartilage that lies anterolateral to the
canal for M. flexor perforans et perforatus digiti II and anteromedial
to the canal for M. flexor perforatus digiti II, then passes through the
bony canal of the hypotarsus that is deep to all the other flexor
tendons; the tendon ossifies again and lies adjacent (lateral) to the
posterior metatarsal crest; the vinculum from the tendon of M. flexor
hallucis longus fuses extensively to the superficial surface of the
present tendon a short distance below the midpoint of the
tarsometatarsus; the tendon is considerably broader below this point
than above it. At the level of the first metatarsal, the tendon divides
into three branches (unossified) that diverge, each passing through a
groove on the ventral surface of the subarticular cartilages ventral to
the trochleae, then pass onto the ventral surfaces of digits II, III,
and IV. On _digit IV_ the tendon gives off two dorsal fibro-elastic
slips before attaching to the ventral surface of the ungual phalanx; one
slip attaches to the subarticular cartilage ventral to the third
interphalangeal joint, the other to the subarticular cartilage of the
fourth joint and may also attach in part to the distal end of the fourth
phalanx. On _digit III_ the tendon gives off two dorsal slips before
attaching to the ventral surface of the ungual phalanx; one slip
attaches to the subarticular cartilage of the second interphalangeal
joint, the other to the subarticular cartilage of the third joint and
may also attach in part to the distal end of the third phalanx. On
_digit II_ the tendon gives off one dorsal slip before attaching to the
ventral surface of the ungual phalanx; the slip attaches to the
subarticular cartilage of the second interphalangeal joint and may also
attach in part to the distal end of the second phalanx.

INNERVATION.--A branch of the medial division of the tibial nerve
penetrates the medial surface of the posterior head.

INDIVIDUAL VARIATION.--In half the legs, the proximal end of the lateral
head is notched for the passage of the peroneal nerve; the main part of
the head lies medial to this nerve; the short fleshy slip lateral to
this nerve arises by a long, slender, and extremely weak tendon from
connective tissue surrounding the femorotibiotarsal joint. In one leg, a
bundle of fibers separates from the lateral head and attaches to the
terminal four mm. of the anterior (proximal) edge of the tendon of M.
extensor iliofibularis. Each of the following variations occurs in
several legs: a third dorsal slip on digit IV attaches to the distal end
of the fourth phalanx in some legs and to the subarticular cartilage of
the fourth joint in other legs; a third dorsal slip on digit III
attaches to the distal end of the third phalanx in some legs and to the
subarticular cartilage of the third joint in other legs; a second dorsal
slip on digit II attaches to the distal end of the second phalanx in
some legs and to the subarticular cartilage of the second joint in other
legs.

_T. cupido_

INDIVIDUAL VARIATION.--The dorsal slips of insertion show variations
similar to those noted above for _T. pallidicinctus_.

_P. p. jamesi_

INDIVIDUAL VARIATION.--In one leg, the proximal end of the lateral head
is notched for the passage of the peroneal nerve. The dorsal slips of
insertion show variations similiar to those given above for _T.
pallidicinctus_. In four legs, a tiny vinculum extends from the lateral
edge of the branch of the tendon on digit IV to the lateral edge of the
underlying medial branch of the tendon of M. flexor perforatus digiti IV
at the level of the second phalanx.


=_M. Popliteus_=, Fig. 19B

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Extremely short but relatively broad
and thick; on posterior surface of proximal end of tibiotarsus;
extending distomedially from proximal part of fibula; deep to M. flexor
hallucis longus; lateral end overlapped by, and fused to, posterior head
of M. flexor digitorum longus; medial end often slightly overlapped by,
and fused to, M. plantaris; medial end (insertion) much wider than
lateral end (origin).

ORIGIN.--The origin is fleshy and tendinous (superficial surface) from
the medial surface of the fibula near the proximal end.

INSERTION.--The attachment is fleshy to the posterior surface of the
proximal end of the tibiotarsus adjacent (lateral) to the origin of M.
plantaris.

INNERVATION.--A branch of the medial division of the tibial nerve
penetrates the posterior surface.

INDIVIDUAL VARIATION.--None of significance in any of the three species
studied.


=_M. Peroneus Longus_=, Figs. 12, 13

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Large; on anterolateral surface of
shank; bounded medially by M. gastrocnemius pars interna and
posterolaterally by Mm. flexor perforans et perforatus digiti III and
flexor perforans et perforatus digiti II; proximal three fourths of
posteromedial part (covered by M. gastrocnemius pars interna)
aponeurotic and tightly fused to medial surfaces of underlying Mm.
tibialis anticus and extensor digitorum longus; proximal part of fleshy
belly somewhat fused to anterior surface of underlying M. tibialis
anticus; posterolateral surface strongly fused to aponeurotic medial
head of M. flexor perforans et perforatus digiti II and slightly fused
to anterolateral edge of M. flexor perforans et perforatus digiti III.

ORIGIN.--The muscle arises by fleshy and tendinous fibers from the edges
of the inner an

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