SUMMARY
Reading edition
The muscles and nerves were dissected in eight legs of the Lesser Prairie Chicken (Tympanuchus pallidicinctus), six legs of the Greater Prairie Chicken (T. cupido pinnatus), three legs of Attwater's Prairie Chicken (T. c. attwateri), and six legs of the Sharp-tailed Grouse (Pedioecetes phasianellus jamesi) for the purpose of obtaining information on individual variation as well as variation between these closely related species. Relatively little information is available regarding the nerves of the leg of birds and little is known about individual variation and variation between closely related forms in the muscles of the leg of birds.
All osteological terms used in the present paper are defined and those of the pelvis are illustrated. New terms were coined for some structures for which no names could be found in the literature. Terms were also coined for the major divisions of the femoral and sciatic nerves. With three exceptions, my muscle terminology follows that of Fisher (1946) and Fisher and Goodman (1955). Their term femoritibialis externus is not used here; the muscle so named is considered to be a part of M. vastus lateralis. Fisher's accessory head of M. flexor cruris lateralis is considered to be a distinct muscle—M. femorocruralis. Usage of the term obturator internus is avoided because the muscle so named is considered not to be homologous with the mammalian muscle of the same name; the entire obturator complex is called M. obturator, and is subdivided into four parts.
The typical (most common) condition of the nerves and muscles in Tympanuchus pallidicinctus is described in detail. Variations from this condition among the other birds studied are then described. All muscles of one leg of T. pallidicinctus are illustrated. Several variations in the muscles are also illustrated. The lumbosacral plexus and nerves of the leg in several specimens that show variations are illustrated.
Considerable individual variation was found in both the muscles and the nerves of the leg of the species studied. Certain muscles were more variable than others. Mm. flexor digitorum longus, obturator, caudofemoralis, and extensor hallucis longus showed the greatest number of variations. Mm. vastus medialis, femoritibialis internus, flexor perforatus digiti III, extensor brevis digiti III, and abductor digiti IV did not exhibit any variations considered significant. Certain legs showed a greater number of variations from the typical condition than did others.
Although most of the variations were minor, some were major. M. extensor proprius digiti III was present in two legs of Pedioecetes but absent in the other legs studied. A fleshy muscle slip connected M. caudofemoralis pars caudifemoralis with the tendinous raphe between Mm. flexor cruris lateralis and femorocruralis in two legs, whereas in others this connection was tendinous or even absent altogether. M. flexor cruris lateralis had an accessory slip arising from the caudal musculature in one leg. A vinculum connected the insertional tendons of Mm. flexor perforans et perforatus digiti II and flexor perforatus digiti II in one leg.
In most specimens there was as much variation between the muscles of the right and left legs of one individual as there was between individuals. The same was true for the nerves, except for the lumbosacral plexus, in which there was no significant variation between the right and left sides of any individual. The peroneal and obturator nerves varied less than the other nerves.
No constant differences in the muscles or nerves was found between T. cupido pinnatus and T. c. attwateri. One constant difference was found between T. cupido and T. pallidicinctus: the fleshy origin of M. extensor iliotibialis lateralis in T. cupido was thicker (associated with a thicker edge of the lateral iliac process).
Although no constant differences in the nerves were found between Pedioecetes and Tympanuchus (both species), 17 constant differences in the muscles were found between these two genera. Study of additional specimens possibly would show enough individual variation in some of these differences to reduce the number of constant differences to fewer than 17. Seven of these differences pertain to features of a single muscle—M. flexor cruris medialis. Some of the other differences are associated with the thinner and much less pronounced lateral iliac process in Pedioecetes. The picture of the differences between Tympanuchus and Pedioecetes that this study presents is radically different from that presented by the study of Hudson, et al. (1959).
The important differences in innervation between previous studies and the present one are discussed.
All of the muscles under consideration have been grouped as either dorsal or ventral muscles, according to their embryonic origin, as described by Romer (1927) and Wortham (1948). This grouping probably represents accurately the phylogenetic origin of these muscles. The dorsal muscles probably were originally supplied by dorsal nerves—the femoral and peroneal—and the ventral muscles probably were originally supplied by ventral nerves—the obturator and tibial. This primitive muscle-nerve relationship has been relatively constant.
Several previous workers have reported some dorsal muscles supplied by ventral nerves and vice versa. Those findings should be viewed with suspicion until verified, because the proximal parts of the tibial and peroneal nerves are intimately associated and their relationship is easily misinterpreted. I found a branch of the tibial nerve that is closely associated with, and distributed with, the peroneal nerve. That branch of the tibial nerve has been mistakenly considered a part of the peroneal nerve by some workers. My study revealed no definite exceptions to the expected innervation.
Table 1. Synonymy of the Muscles of the Leg of Birds
Gadow (1891) Hudson (1937) Howell (1938) Fisher & Goodman (1955) Holmes
ilio-tibialis ilio-tibialis extensor iliotibialis lateralis extensor ilio-tibialis lateralis extensor iliotibialis lateralis
ilio-tibialis internus s. sartorius sartorius extensor iliotibialis anterior extensor ilio-tibialis anterior extensor iliotibialis anticus
ambiens ambiens ambiens ambiens ambiens
femori-tibialis externus ............ femori-tibialis externus ............ vastus lateralis femoritibialis externus vastus lateralis (a) pars postica (b) pars lateralis
{ femori-tibialis { medius { { vastus lateralis
femori-tibialis medius } { } vastus medialis { } { vastus medialis vastus medialis
femori-tibialis internus femori-tibialis internus femoritibialis internus femoritibialis internus
ilio-fibularis biceps fernoris extensor iliofibularis extensor ilio-fibularis extensor iliofibularis
ilio-femoralis externus glutaeus medius et minimus piriformis piriformis piriformis
ilio-trochantericus posterior ilio-trochantericus posterior gluteus profundus gluteus profundus gluteus profundus
ilio-trochantericus anterior ilio-trochantericus anterior iliacus iliacus iliacus
ilio-trochantericus medius ilio-trochantericus medius ............ ilio-trochantericus medius iliotrochantericus medius
ilio-femoralis internus iliacus psoas psoas psoas
caud ilio flexorius semitendinosus flexor cruris lateralis flexor cruris lateralis (a) main head (b) accessory heads flexor cruris lateralis
accessorius semitendinosi accessorius semitendinosi femorocruralis femorocruralis
ischio-flexorius semimembranosus flexor cruris medialis flexor cruris medialis flexor cruris medialis
caud-ilio-femoralis (a) pars caudi-femoralis (b) pars ilio-femoralis piriformis (a) pars caudi-femoralis (b) pars ilio-femoralis caudofemoralis caudofemoralis (a) pars caudi-femoralis (b) pars ilio-femoralis caudofemoralis (a) pars caudifemoralis (b) pars iliofemoralis
flexor iliofemoralis
ischio-femoralis ischio-femoralis flexor ischiofemoralis flexor ischiofemoralis flexor ischiofemoralis
{ pub-ischio-femoralis { { adductor longus et brevis (a) pars anterior (b) pars posterior adductor superficialis adductor superficialis adductor superficialis
adductor profundus adductor profundus adductor profundus
obturator obturator internus } { } obturator { } { obturator internus } } obturator }
accessorii M. obturatoris obturator externus obturator externus
gastrocnemius gastrocnemius gastrocnemius gastrocnemius
flexor perforans et perforatus digiti II flexor perforans et perforatus digiti II flexor perforans et perforatus digiti II flexor perforans et perforatus digiti II
flexor perforans et perforatus digiti III flexor perforans et perforatus digiti III flexor perforans et perforatus digiti III flexor perforans et perforatus digiti III
flexor perforatus digiti IV flexor perforatus digiti IV flexor perforatus digiti IV flexor perforatus digiti IV
flexor perforatus digiti III flexor perforatus digiti III flexor perforatus digiti III flexor perforatus digiti III
flexor perforatus digiti II flexor perforatus digiti II flexor perforatus digiti II flexor perforatus digiti II
flexor hallucis longus flexor hallucis longus flexor hallucis longus flexor hallucis longus
plantaris plantaris plantaris plantaris
flexor profundus s. perforans flexor digitorum longus flexor digitorum longus flexor digitorum longus
popliteus popliteus popliteus popliteus
peroneus superficialis peronaeus longus peroneus longus peroneus longus
tibialis anticus tibialis anterior tibialis anterior tibialis anticus
extensor digitorum communis extensor digitorum longus extensor digitorum longus extensor digitorum longus
peroneus profundus peronaeus brevis peroneus brevis peroneus brevis
extensor hallucis brevis extensor hallucis longus extensor hallucis longus extensor hallucis longus
abductor digiti II abductor digiti II abductor digiti II abductor digiti II—
extensor brevis digiti III } { } extensor proprius { } digiti III { } { extensor brevis digiti III extensor brevis digiti III
extensor brevis digiti IV extensor brevis digiti IV extensor brevis digiti IV
flexor brevis digiti III lumbricalis ............ lumbricalis
abductor digiti IV abductor digiti IV abductor digiti IV abductor digiti IV
flexor hallucis brevis flexor hallucis brevis flexor hallucis brevis flexor hallucis brevis
adductor digiti II adductor digiti II adductor digiti II ............
adductor digiti IV adductor digiti IV ............ ............
Table 2. Relative Sizes (in Percentages) of Some Muscles in Tympanuchus and Pedioecetes
Muscle Tympanuchus Pedioecetes
Iliacus: width of fleshy origin (divided by length of ilium) .10 .08-.11 13 .19 .17-.19 6
Flexor cruris lateralis: maximum width of exposed part (divided by length of ilium) .22 .19-.27 13 .31 .27-.36 6
Flexor cruris medialis: width of origin (divided by length of ilium) .11 .08-.16 13 .22 .19-.23 6
Flexor cruris medialis: width of insertion (divided by length of tibiotarsus) .09 .08-.13 13 .17 .15-.17 4
Adductor superficialis: width of origin (divided by length of ilium) .20 .17-.23 13 .13 .10-.16 5
Femorocruralis: distance of proximal end of origin from proximal end of femur (divided by length of femur) .59 .55-.63 13 .40 .38-.43 6
Extensor digitorum longus: length of fleshy belly (divided by length of tibiotarsus) .73 .64-.83 13 .59 .50-.62 4
FOOTNOTES:
Table 3. Occurrence of Individual Variations in Muscles
T.p. T.c.p. T.c.a. P.p.
1 L 1 R 2 L 2 R 3 L 3 R 4 L 5 R 1 L 1 R 2 L 2 R 3 L 4 L 1 L 1 R 2 L 1 L 1 R 2 L 3 L 3 R 4 L
Ambiens
origin partly fleshy x
Vastus lateralis
no vincula x x
Extensor iliofibularis
insertional tendon double x
Piriformis
posteroproximal corner tendinous x x x x x
insertion fused to flexor ischiofemoralis x
Iliotrochantericus medius
not notched x x x
anterior part with fleshy origin x x x x
insertion fused to gluteus profundus x
muscle split x
Flexor cruris lateralis
accessory slip present x
Flexor cruris medialis
origin from pubis x x
insertion partly fleshy x x x x
insertional tendon split x
Caudofemoralis
accessory slip fleshy x x
tendinous area in belly of pars caudifemoralis x x x
origin from pubis x
insertion entirely tendinous x
Flexor ischiofemoralis
insertion partly fleshy x x x
Adductor superficialis
groove for flexor cruris medialis present x x x x
completely fused with adductor profundus x
Adductor profundus
proximal part of insertion tendinous x
distal end of insertion tendinous x
Obturator
independent slip of pars antica present x x
slip of pars antica fused to pars postica x x
independent slip of pars dorsalis present x x x x
pars dorsalis fused with pars antica x
Gastrocnemius
pars interna overlaps peroneus longus x
Flexor perforans et perforatus digiti II
anterior head entirely tendinous x
vinculum joins flexor perforatus digiti II x
origin from superficial surface of patellar tendon x
Flexor perforans et perforatus digiti III
accessory head present x x
Flexor perforatus digiti II
roof of hypotarsal canal bony x x x
Plantaris
accessory head present x
origin from medial collateral ligament x
Flexor digitorum longus
notched for peroneal nerve x x x x x
origin from tendon of extensor iliofibularis x
third dorsal slip present in digiti IV x x x x x x x x x
third dorsal slip present in digiti III x x x x x x x x x x x x
second dorsal slip present in digiti II x x x x x x x x x x x x
vinculum joins flexor perforatus digiti IV x x x x
Peroneus longus
origin from patellar tendon x x x x x
Tibialis anticus
accessory insertion absent x x
Extensor digitorum longus
lateral branch of tendon not ossified x x x x x x x x x x
origin from posterior surface of outer cnemial crest x x x
Extensor hallucis longus
origin lateral to retinaculum x x
distal fibers of distal head insert independently x x x x x
accessory bundle present x
entire distal head inserts independently x
Abductor digiti II
accessory insertion present x
Extensor proprius digiti III
present x x
Table 4. Number of Muscular Variations in Common Between the Legs Studied
Leg Other leg of same specimen T.p. T.c.p. T.c.a. P.p. No other legs
1 L 1 R 2 L 2 R 3 L 3 R 4 L 4 R 1 L 1 R 2 L 2 R 3 L 4 L 1 L 1 R 2 L 1 L 1 R 2 L 3 L 3 R 4 L
T.p. 1 L 1 — — 2 2 1 1 1 1 2 1 1 2 1
T.p. 2 R 6 — — 2 1 1 2 1 1 1 2 3 3 3 2 3 1 1 4 2 0
T.p. 3 L 4 2 1 2 2 — — 1 1 1 2 3 2 2 4 4 1 2 3 5 1
T.c.p. 1 R 1 1 — — 1 2
T.c.p. 2 R 0 1 1 1 — — 2 1 1 1 1 1 1 1 3
T.c.a. 1 R 5 1 3 3 2 1 1 1 2 2 — — 3 3 4 1 1 3 2 3
P.p. 1 L 4 2 2 2 3 1 1 1 3 3 3 2 — — 3 2 3 7 2
P.p. 3 R 4 4 4 2 2 1 1 1 1 2 3 3 3 3 5 4 — — 5 1
Table 5. Occurrence of Individual Variations in Nerves
T.p. T.c.p. T.c.a. P.p.
1 L 1 R 2 L 2 R 3 L 3 R 4 L 5 R 1 L 1 R 2 L 2 R 3 L 4 L 1 L 1 R 2 L 1 L 1 R 2 L 3 L 3 R 4 L
Lumbosacral plexus
two fureal nerves x x x x x x x
S9 with three branches x
prefixed x x x x x x x x
sciatic nerve with six roots x x x x x x x x x x
obturator nerve from S2 and S3 only x x x x
femoral nerve mainly from S2-S4 x x x x x x x x
Femoral nerve
anterior division innervates extensor iliotibialis lateralis x x x x x
dorsal division fused with anterior division x x x x
dorsal division fused with middle division x x x x x x
two branches to iliacus x x
middle division anastomoses with anterior division x x x x x
anterodorsal division does not go through femoral notch x x
branch of anterior division perforates iliacus x
cutaneous branch perforates extensor iliotibialis lateralis x x
branch of middle division perforates vastus medialis x
branch to vasti innervates extensor iliotibialis lateralis x
anterior branch of anterior division cutaneous x x x
Sciatic nerve
twig to pars caudifemoralis independent x
branch to flexor cruris lateralis does not perforate caudofemoralis x x x x x x x x x
paraperoneal nerve enters peroneal sheath x x x x x x
cutaneous peroneal branch perforates gastrocnemius pars externa x x x
cutaneous peroneal branch absent x x x
distal cutaneous tibial branch absent x
twig to tail present x x x x x x x
nonmuscular peroneal twig deep to vastus lateralis pars postica x x x x
branch to flexor cruris medialis from posterior tibial division x x x
extra twigs join cutaneous tibial branches x
branch to flexor cruris medialis an independent division x x x
branch to flexor cruris medialis perforates flexor ischiofemoralis x
two twigs to flexor ischiofemoralis x x x x x
independent extra branch innervates extensor iliofibularis x
branch to femorocruralis innervates gastrocnemius pars media x
Peroneal nerve
superficial and deep peroneal nerves do not join x x x x
Tibial nerve
independent extra branch innervates flexor perforatus digiti IV x x
anastomosis involving posterior division x x
branch to gastrocnemius pars externa an independent division x
branch to gastrocnemius pars media innervates femorocruralis x x
extra branch innervates flexor perforatus digiti III x x
branch to gastrocnemius pars interna perforates plantaris x
branch to gastrocnemius pars interna innervates plantaris x
Table 6. Number of Nerve Variations in Common Between the Legs Studied
Leg Other leg of same specimen T.p. T.c.p. T.c.a. P.p. No other legs
1 L 1 R 2 L 2 R 3 L 3 R 4 L 5 R 1 L 1 R 2 L 2 R 3 L 4 L 1 L 1 R 2 L 1 L 1 R 2 L 3 L 3 R 4 L
T.p. 1 L 1 — — 1 2 1 1 2 1 1 1 1 1 1 1 1 2 1 2 0
T.p. 2 L 5 1 — — 2 1 3 1 2 2 2 1 2 1 2 1 1
T.p. 3 R 3 1 2 1 — — 1 1 1 1 1 1 1 1 1
T.c.p. 1 R 1 1 1 1 1 1 — — 2 1 2 1 0
T.c.p. 2 L 2 1 1 1 1 1 1 2 — — 2 1 1
T.c.a. 1 R 1 2 1 1 1 1 — — 1 1 1 2
P.p. 1 R 3 2 2 1 1 1 1 1 1 1 — — 1 2 2 3 1
P.p. 3 L 2 1 2 1 1 1 2 3 — — 2 2