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

by E. Bruce Holmes

Individual Variation.—In all the legs except one, an additional twig arises from the branch to M. flexor cruris medialis and penetrates the lateral surface of M. flexor ischiofemoralis. The ventral part of the insertion is fleshy in one leg.

M. Adductor Superficialis (M. adductor longus et brevis, pars externa), Figs. 14, 16, 17

T. pallidicinctus

General Description and Relations.—Posterior to femur, lateral to M. adductor profundus, and medial to Mm. flexor ischiofemoralis, caudofemoralis, and femorocruralis; proximal end (fleshy) fused to proximal tendinous end of M. adductor profundus.

Origin.—The origin is fleshy and tendinous from the proximal end of the lateral surface of M. adductor profundus and from a narrow line on the ischium adjacent (dorsal) to the origin of the latter; the posterior part of the origin sometimes extends farther dorsally on the lateral surface of the ischium; the origin does not extend so far anteriorly nor so far posteriorly as the origin of M. adductor profundus; the anterior edge is at the posterior border of the obturator foramen.

Insertion.—The attachment is fleshy and thick (distal end thin) to the posterior surface of the middle part of the femur between the posterior and posterolateral intermuscular lines; the attachment is adjacent (lateral) to the insertion of M. adductor profundus and adjacent (medial) to the origins of Mm. vastus lateralis (proximally) and femorocruralis (distally); the proximal edge is approximately at the level of the distal edge of the insertion of M. caudofemoralis.

Innervation.—A branch of the obturator nerve emerges from the obturator foramen dorsal to the tendon of insertion of M. obturator pars postica, turns ventrally (crossing latter), and passes deep to the anteroproximal corner of M. adductor superficialis, extending posterodistally between the adductor muscles and giving twigs to the medial surface of M. adductor superficialis and to the lateral surface of M. adductor profundus.

Individual Variation.—The anterior edges of the two adductor muscles are so firmly fused together in some cases that the boundaries cannot be identified at this point. In several legs, there is a deep longitudinal groove in the posterior edge of the proximal part of the muscle into which the anterior edge of M. flexor cruris medialis fits.

T. cupido

Individual Variation.—In some cases, the anterior edges of the two adductor muscles are firmly fused together.