Variation in the Muscles and Nerves of the Leg in Two Genera of Grouse Part 7

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 pa.s.sage 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); pa.s.ses 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. transversoa.n.a.lis) 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 pa.s.ses 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 pa.s.ses 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 pa.s.ses 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_