Variation in the Muscles and Nerves of the Leg in Two Genera of Grouse Part 4

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)

[Ill.u.s.tration: 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_

[Ill.u.s.tration: 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.

[Ill.u.s.tration: 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.]

[Ill.u.s.tration: 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 a.s.sociate 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 pa.s.ses 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 pa.s.ses 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.

[Ill.u.s.tration: 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 pa.s.s 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.

[Ill.u.s.tration: 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_

[Ill.u.s.tration: 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 p.r.o.nounced lateral iliac process. The distal accessory aponeurosis is absent.

[Ill.u.s.tration: 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.

[Ill.u.s.tration: 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.