Variation in the Muscles and Nerves of the Leg in Two Genera of Grouse (Tympanuchus and Pedioecetes)

by E. Bruce Holmes

P. p. jamesi

Individual Variation.—Pars lateralis often begins proximally at the level of the insertion of M. piriformis.

M. Vastus Medialis (Part of M. femoritibialis medius), [Figs. 13], [14], [15]

T. pallidicinctus

General Description and Relations.—Thick; on anteromedial surface of femur medial to anterior part of M. vastus lateralis pars lateralis; bounded medially by Mm. ambiens and extensor iliotibialis anticus (distally); bounded posteromedially by M. femoritibialis internus; proximal part medial to posterior ends of Mm. iliacus, iliotrochantericus medius, and gluteus profundus; lateral surface, except proximal part, fused with anterior part of M. vastus lateralis pars lateralis; part of lateral surface of M. vastus medialis covered by sheet of fascia attaching to anterior intermuscular line; M. vastus lateralis separable from this fascia, but fascia absent anteriorly and distally and these two muscles indistinguishably fused.

Origin.—The proximal third is attached narrowly by its lateral edge; the distal two thirds is attached broadly by its entire deep surface. The proximal third arises tendinously from the trochanteric ridge and the proximal end of the anterior intermuscular line and fleshily from a narrow area of the femur adjacent (medial) to the latter; the distal part arises tendinously from the anterior intermuscular line and fleshily from a broad adjacent area on the anteromedial surface of the femur, terminating distally at the level of the proximal end of the internal condyle; the posterior edge contacts the origin of M. femoritibialis internus.

Insertion.—Attachment is in common with M. vastus lateralis pars lateralis, which see.

Innervation.—Two or more branches of the middle division of the femoral nerve penetrate the anterior surface of the fused Mm. vastus medialis and vastus lateralis pars lateralis; a variable number of branches of the same division penetrate the medial surface of the proximal part of M. vastus medialis.

Individual Variation.—None of significance in any of the three species studied.