Chapter I: Part 1

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 this series by addressing the Exchange Librarian, University of Kansas Library, Lawrence, Kansas. Copies for individuals, persons working in a particular field of study, may be obtained by addressing instead the Museum of Natural History, University of Kansas, Lawrence, Kansas. There is no provision for sale of this series by the University Library, which meets institutional requests, or by the Museum of Natural History, which meets the requests of individuals. Nevertheless, when individuals request copies from the Museum, 25 cents should be included, for each separate number that is 100 pages or more in length, for the purpose of defraying the costs of wrapping and mailing.

* 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

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.

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.