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

by E. Bruce Holmes

T. cupido

Individual Variation.—The relationship between the two heads varies as follows: the proximal end of the distal head may be fused to the distal end of the belly of the proximal head; the proximal end of the distal head may begin anterior (adjacent) to the distal end of the belly of the proximal head; there may be a distinct gap between the fleshy parts of the two heads. In two legs, there is no origin from the insertion of M. tibialis anticus. In one leg, a small accessory bundle of fleshy fibers arises from the proximal end of the first metatarsal (widely separated from the origin of the distal head), passes through the retinaculum deep to the common tendon and attaches to the dorsal surface of the articular capsule of the metatarsophalangeal joint; thus this bundle is completely separate from the remainder of the muscle. In two legs, the same nerve branch that gives twigs into the proximal head also gives off (much farther distally) a twig that enters the distal head.

P. p. jamesi

Individual Variation.—The proximal end of the distal head may begin anterior (adjacent) to the distal end of the belly of the proximal head. In four legs, the origin of the proximal head does not extend proximally medial to the retinaculum for M. extensor digitorum longus; in one of these legs, a part of the proximal end extends proximally lateral to this retinaculum. The distalmost fibers of the distal head do not join the common tendon but insert independently on the dorsal surface of the articular capsule of the metatarsophalangeal joint in four legs; in another leg, the entire distal head has the latter insertion (consequently the two heads are completely separate).

M. Abductor Digiti II [Figs. 19]E, [20]N

T. pallidicinctus

General Description and Relations.—Short; on medial surface of distal part of tarsometatarsus; proximal end adjacent (anterior) to distal head of M. extensor hallucis longus.

Origin.—The origin is fleshy from the medial surface of the distal part of the tarsometatarsus anterior (adjacent) to the first metatarsal and from the anteromedial surface of the basal half of the first metatarsal.

Insertion.—The flat tendon passes over the medial surface of the trochlea for digit II and attaches to the medial surface of the proximal end of the first phalanx of digit II; the tendon is fused with the articular capsule.