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

by E. Bruce Holmes

Insertion.—The short, slender, ossified tendon becomes flexible and passes through the canal in the tibial cartilage that lies medial to the canal for M. flexor hallucis longus and lateral to the canals for Mm. flexor digitorum longus and flexor perforans et perforatus digiti II. The tendon passes with the tendon of M. flexor perforans et perforatus digiti II (lateral to latter) through the canal in the hypotarsus that is deep to the groove for M. flexor perforatus digiti III and superficial to the canal for M. flexor digitorum longus; the former canal has a bony floor and sides but a fibrous roof; a fibrous partition subdivides the proximal half of this canal, forming a separate channel for each tendon. The tendon is ossified for most of the length of the tarsometatarsus and is situated lateral (adjacent) to the posterior metatarsal crest; immediately below the hypotarsus, the tendon becomes situated deep to the tendon of M. flexor perforans et perforatus digiti II and farther distally becomes situated medial and finally superficial to the latter; at the distal end of the tarsometatarsus the tendon expands greatly and its edges (thick) pass dorsally around the underlying flexor tendons and become continuous with the subarticular cartilage ventral to the trochlea for digit II. The tendon extends onto the ventral surface of digit II and attaches by its edges to the ventromedial and ventrolateral surfaces of the proximal part of the first phalanx (the lateral edge extending farthest distally); the tendons of Mm. flexor perforans et perforatus digiti II and flexor digitorum longus emerge from the distal end of the tendon of M. flexor perforatus digiti II.

Innervation.—The posterior division of the tibial nerve passes between the medial heads of Mm. flexor perforatus digiti III and flexor perforatus digiti IV and gives a twig to the superficial surface of each of the three heads of M. flexor perforatus digiti II and sometimes gives another twig to the superficial surface of the distal part of the common belly.

Individual Variation.—In one leg, a vinculum connects the tendon with that of M. flexor perforans et perforatus digiti II (which see).

T. cupido

Individual Variation.—The canal in the hypotarsus through which the tendon passes has a bony (instead of fibrous) roof in one leg.

P. p. jamesi

Individual Variation.—The variation given above for T. cupido is found in both legs of one specimen.

M. Flexor Hallucis Longus, [Figs. 15], [19]A

T. pallidicinctus