Variation in the Muscles and Nerves of the Leg in Two Genera of Grouse Part 14

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Short and relatively broad (narrow proximally); on mid-anterior surface of distal part of tarsometatarsus; tendon of insertion fused with articular capsule.

ORIGIN.--The origin is fleshy from the mid-anterior surface of the distal part of the tarsometatarsus ending a short distance proximal to the trochlea for digit III.

INSERTION.--The flat tendon pa.s.ses over the trochlea for digit III and attaches to the dorsal surface of the proximal end of the first phalanx of digit III.

INNERVATION.--The compound nerve formed by the fusion of a branch of the superficial peroneal nerve with a branch of the deep peroneal nerve gives a twig to the proximal end of the muscle.

INDIVIDUAL VARIATION.--In some cases, the twig arises from the deep peroneal branch alone (which is not joined by the superficial peroneal nerve). The individual variation is insignificant in _T. cupido_ and _P.

p. jamesi_.

=_M. Extensor Proprius Digiti III_= (Not found by Hudson, _et al._), Fig. 20N

_T. pallidicinctus_ and _T. cupido_

Absent in both species.

_P. p. jamesi_

This atypical muscle was found in only two legs (P.p. 1L and 4L). The following description applies to P.p. 4L (Fig. 20N).

GENERAL DESCRIPTION AND RELATIONS.--Small but well developed; fleshy part 1-1/2 13 mm.; proximal end narrower; on mid-anterior surface of tarsometatarsus between Mm. extensor brevis digiti IV and extensor hallucis longus and mostly proximal to M. extensor brevis digiti III; tendinous distal part superficial to latter; fleshy belly ending immediately distal to proximal end of latter.

ORIGIN.--The origin is fleshy from a narrow elongate area on the mid-anterior surface of the tarsometatarsus between Mm. extensor brevis digiti IV and extensor hallucis longus, beginning at the distal end (bony) of the elongate accessory insertion of M. tibialis anticus. The distal part of the belly is free.

INSERTION.--The attachment is by a thin, wide (relative to belly) tendon to the superficial surface of M. extensor brevis digiti III.

INNERVATION.--Not found.

INDIVIDUAL VARIATION.--In P.p. 1L, the muscle is less well developed.

The fleshy belly is 1 5 mm. It arises from the lateral edge of M.

extensor hallucis longus. The extremely slender insertional tendon attaches as above.

=_M. Extensor Brevis Digiti IV_=, Figs. 19E, 20N

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Slender and tapering; on lateral part of anterior surface of tarsometatarsus; length of belly variable; middle of medial edge in contact with M. extensor hallucis longus.

ORIGIN.--The origin is fleshy from the lateral part of the anterior surface of the tarsometatarsus, including the anterior metatarsal groove.

INSERTION.--The long slender tendon enters the anterior aperture of the distal foramen, pa.s.ses through the intertrochlear ca.n.a.l, emerges from the terminal foramen, and attaches to the medial surface of the proximal end of the first phalanx of digit IV.

INNERVATION.--The superficial peroneal branch of the peroneal nerve sends a twig into the proximal part of the muscle.

INDIVIDUAL VARIATION.--None of significance in any of the three species studied.

=_M. Lumbricalis_=, Fig. 19F

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Small, thin, and strap-shaped; on mid-posterior surface of distal end of tarsometatarsus deep to tendon of M. flexor digitorum longus; belly partly fleshy and partly elastic connective tissue.

ORIGIN.--The muscle arises from the deep (anterior) surface of the tendon of M. flexor digitorum longus a short distance proximal to the trifurcation of the latter.

INSERTION.--The muscle attaches to the proximal end of the subarticular cartilage ventral to the trochlea for digit III.

INNERVATION.--A long but extremely small twig arises from the paraperoneal branch of the tibial nerve a short distance distal to the hypotarsus and extends distally along the mid-posterior surface of the tarsometatarsus (parallel to a larger nonmuscular branch) and enters the deep surface distal to the middle. It was possible to follow this twig in only two legs; it was presumably destroyed in the course of dissection in the others.

INDIVIDUAL VARIATION.--In some cases, the "muscle" appears grossly to be entirely connective tissue, although a distinct ent.i.ty.

_T. cupido_

INDIVIDUAL VARIATION.--In some cases, the "muscle" appears grossly to be entirely connective tissue. The innervation was found in only one leg, in which the twig arises more distally than in _T. pallidicinctus_.

_P. p. jamesi_

The innervation was not found.

=_M. Abductor Digiti IV_=, Fig. 19F

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Slender and elongate; on posterior surface of tarsometatarsus lateral to midline; in contact with M. flexor hallucis brevis in midline.

ORIGIN.--The origin is fleshy from the posterior surface of the tarsometatarsus lateral to the midline beginning near the proximal end (lateral to the hypotarsus) and ending at the level of the first metatarsal.

INSERTION.--The slender tendon, which begins along the lateral edge of the distal part of the belly, pa.s.ses through a retinaculum on the posterolateral surface of the tarsometatarsus immediately above the outer trochlea and attaches to the lateral surface of the proximal end of the first phalanx of digit IV.

INNERVATION.--The paraperoneal branch of the tibial nerve gives one or two twigs to the proximal part of the muscle.

INDIVIDUAL VARIATION.--None of significance in any of the three species studied.

=_M. Flexor Hallucis Brevis_=, Fig. 19F

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Slender and elongate; on posterior surface of tarsometatarsus medial to midline; belly (except proximal end) adjacent (lateral) to posterior metatarsal crest; proximal end pa.s.sing under latter (immediately distal to hypotarsus) and lying anteromedial to hypotarsus.

ORIGIN.--The origin is fleshy from the medial metatarsal depression and from the posterior surface of the tarsometatarsus between the midline and the posterior metatarsal crest beginning immediately below the hypotarsus and ending a short distance above the first metatarsal (sometimes more proximally).

INSERTION.--The slender tendon, which begins along the medial edge of the distal part of the belly, pa.s.ses through the groove on the posterodistal surface of the first metatarsal and onto the proximal end of the ventral surface of the hallux; the tendon widens considerably and attaches by its edges to the ventral surface of the proximal end of the first phalanx, forming a short "tunnel" through which the tendon of M.

flexor hallucis longus pa.s.ses.