Individual Variation.—In one leg the insertion is partly fleshy. The posterior division of the femoral nerve perforates the muscle in one instance.
M. Flexor Cruris Lateralis (M. semitendinosus), [Figs. 12], [13], [14], [15], [16], [17]
This muscle represents only the main head of the muscle for which Fisher and Goodman (1955) used the same name. Their accessory head of M. flexor cruris lateralis is here termed M. femorocruralis.
T. pallidicinctus
General Description and Relations.—Large, thick, and strap-shaped; on posterior surface of thigh; proximal part bounded anteriorly by Mm. extensor iliotibialis lateralis and extensor iliofibularis; anterodistal part deep to latter; bounded medially by Mm. caudofemoralis (proximally) and flexor cruris medialis (distally); proximal end much narrower than remainder and posterior to ilium; fused to underlying tough membrane, which forms body wall posterior to ilium; proximal half of narrow part aponeurotic; distal part of muscle posterior to M. femorocruralis; separated from latter by common raphe to which both attach; caudal muscle (M. transversoanalis) attached aponeurotically to superficial surface of posteroproximal fleshy part of M. flexor cruris lateralis.
Origin.—The origin is tendinous (superficial surface) and fleshy from the entire dorsolateral iliac ridge and fleshy from an area of the ilium below this ridge, also tendinous from the posterior edge of the ilium medial to the dorsolateral iliac ridge, and also tendinous from the transverse processes of the first free caudal vertebra and the vertebra either anterior or posterior to the latter.
Insertion.—M. flexor cruris lateralis and M. femorocruralis insert broadly on opposite sides of a long tendinous raphe that extends parallel to, but some distance posterior to, the distal half of the femur; the distal end of this tendon broadens somewhat and fuses to the medial surface of M. gastrocnemius pars media (continuous with the tendon of the latter); the superficial part of this tendon continues toward the tibiotarsus, soon fusing to the deep surface of the overlying tendon of M. flexor cruris medialis; thus the common tendon of M. flexor cruris lateralis and M. femorocruralis insert in common with both M. flexor cruris medialis and M. gastrocnemius pars media.
Innervation.—A branch of the middle tibial division of the sciatic nerve enters the substance of M. caudofemoralis pars iliofemoralis, and emerges near its ventral edge, then passes lateral to M. caudofemoralis pars caudifemoralis and enters the anterior part of M. flexor cruris lateralis.
Individual Variation.—In three legs, the nerve does not perforate M. caudofemoralis pars iliofemoralis, but passes deep to it.
T. cupido