Variation in the Muscles and Nerves of the Leg in Two Genera of Grouse Part 11

_T. cupido_

INDIVIDUAL VARIATION.--None of significance.

_P. p. jamesi_

INDIVIDUAL VARIATION.--In four legs, a tiny vinculum connects with the tendon of M. flexor digitorum longus (which see).

=_M. Flexor Perforatus Digiti III_=, Figs. 13, 14, 15, 16, 17

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Divided into two widely separated heads--medial and anterolateral--with completely separate bellies but with common insertional tendon; small _anterolateral head_ on lateral aspect of thigh deep to M. flexor perforans et perforatus digiti II and posterior to M. flexor digitorum longus; fleshy part of head distolateral to belly of M. flexor perforatus digiti IV; fleshy part fused to lateral edge of belly of M. flexor perforatus digiti II; proximal part of head a slender ossified tendon fused to anterior edge of both fleshy and tendinous parts of anterolateral head of M. flexor perforatus digiti IV and to lateral edge of anterolateral head of M.

flexor perforatus digiti II; this tendon pa.s.sing deep to tendon of insertion of M. extensor iliofibularis and to peroneal nerve; large _medial head_ on posteromedial surface of thigh anterior to medial edge of M. gastrocnemius pars externa, lateral to M. gastrocnemius pars media, and medial to M. flexor perforatus digiti IV; fused to medial surface of medial head of latter and to medial edges of Mm. flexor perforatus digiti II and flexor hallucis longus; proximal end of head tendinous.

ORIGIN.--The _medial head_ attaches tendinously to the medial part of the popliteal area in common with the medial head of M. flexor perforatus digiti II and with the medial edges of Mm. flexor perforatus digiti IV (medial head) and flexor hallucis longus; and is also fused to the articular capsule. The _anterolateral head_ arises in common with the anterolateral heads of Mm. flexor perforatus digiti II and flexor perforatus digiti IV (see account of latter).

INSERTION.--The short unossified tendon of the anterolateral head and the longer ossified tendon of the medial head join (after the latter becomes flexible) a short distance above the tibial cartilage, forming a broad flat common tendon that pa.s.ses posterior to the tibial cartilage (in a shallow groove of the latter); the main part of the tendon is deep to the tendons of Mm. flexor perforatus digiti IV and flexor perforans et perforatus digiti III, but forms separate thin sheaths around these two tendons at the level of the tibial cartilage. A thin sheet of connective tissue covers these three tendons and attaches by its edges to the tibial cartilage, forming a sheath for them. These three tendons pa.s.s through the superficial groove in the hypotarsus deep to the tendon of M. gastrocnemius; the tendon of M. flexor perforatus digiti III is ossified for most of the length of the tarsometatarsus; a short distance below the hypotarsus, the anterior branch of the tendon of M. peroneus longus attaches broadly to the lateral edge of the tendon of M. flexor perforatus digiti III. In the proximal part of the tarsometatarsus the tendon is deep to the tendon of M. flexor perforans et perforatus digiti III, but farther distally becomes medial and then superficial to the latter and lateral to the tendon of M. flexor perforans et perforatus digiti II; near the distal end of the tarsometatarsus a narrow but strong vinculum extends from the lateral edge of the tendon somewhat distally to the lateral edge of the tendon of M. flexor perforans et perforatus digiti III. At the distal end of the tarsometatarsus the tendon expands before entering the ventral surface of digit III where it soon divides into two branches, between which emerge the tendons of Mm.

flexor perforans et perforatus digiti III and flexor digitorum longus; the lateral branch attaches to the subarticular cartilage ventral to the first interphalangeal joint and to the lateral surface of the distal end of the first phalanx; the medial branch has similar attachments on the medial side of the digit.

INNERVATION.--The posterior division of the tibial nerve pa.s.ses between the medial heads of M. flexor perforatus digiti III and M. flexor perforatus digiti IV and sends a twig to the lateral surface of the former, then pa.s.ses deep to the common belly of M. flexor perforatus digiti IV and sends a twig to the posterior surface of the anterolateral head of M. flexor perforatus digiti III.

INDIVIDUAL VARIATION.--None of significance.

_T. cupido_

INDIVIDUAL VARIATION.--In one leg, an extra branch (immediately distal to the branch to M. gastrocnemius pars media) of the medial division of the tibial nerve penetrates the medial surface of the proximal end of the medial head.

_P. p. jamesi_

INDIVIDUAL VARIATION.--None of significance.

=_M. Flexor Perforatus Digiti II_=, Figs. 15, 17

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Bipinnate; on posterior aspect of shank deep to M. flexor perforatus digiti IV and between two heads of M.

flexor perforatus digiti III; bounded anteriorly by Mm. flexor digitorum longus and flexor hallucis longus; proximal part divided into three small heads--medial, lateral, and anterolateral; medial and proximal parts of _medial head_ tendinous and extremely thin except for ossified medial edge; proximal part of _lateral head_ tendinous and lateral to insertional tendon of M. extensor iliofibularis; both tendinous and fleshy parts fused to overlying tendon of M. flexor perforatus digiti IV; narrow _anterolateral head_ fused to overlying anterolateral head of latter muscle and (anterolateral edge) to ossified tendon of anterolateral head of M. flexor perforatus digiti III; lateral edge of common belly fused to latter head; medial edge of muscle fused to medial heads of Mm. flexor perforatus digiti IV and flexor perforatus digiti III and to M. flexor hallucis longus.

ORIGIN.--The _medial head_ attaches by a slender ossified tendon to the medial part of the popliteal area in common with the medial head of M.

flexor perforatus digiti III and with the medial edges of Mm. flexor perforatus digiti IV (medial head) and flexor hallucis longus; this head is also fused to the articular capsule. The above-mentioned ossified part of the tendon is situated at the junction of M. flexor perforatus digiti II and M. flexor perforatus digiti III (medial head) and could be considered to be a part of the latter rather than the former. The flat tendon of the _lateral head_ arises in common with the lateral head of M. flexor perforatus digiti IV (which see). The _anterolateral head_ arises in common with the anterolateral heads of Mm. flexor perforatus digiti IV and flexor perforatus digiti III (see former).

INSERTION.--The short, slender, ossified tendon becomes flexible and pa.s.ses through the ca.n.a.l in the tibial cartilage that lies medial to the ca.n.a.l for M. flexor hallucis longus and lateral to the ca.n.a.ls for Mm.

flexor digitorum longus and flexor perforans et perforatus digiti II.

The tendon pa.s.ses with the tendon of M. flexor perforans et perforatus digiti II (lateral to latter) through the ca.n.a.l in the hypotarsus that is deep to the groove for M. flexor perforatus digiti III and superficial to the ca.n.a.l for M. flexor digitorum longus; the former ca.n.a.l has a bony floor and sides but a fibrous roof; a fibrous part.i.tion subdivides the proximal half of this ca.n.a.l, 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) pa.s.s 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 pa.s.ses 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 ca.n.a.l in the hypotarsus through which the tendon pa.s.ses 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, 19A

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Elongate and tapering; on posterior aspect of shank deep to M. flexor perforatus digiti II and to proximal end of medial head of M. flexor perforatus digiti IV; bounded anterolaterally by M. flexor digitorum longus and anteromedially by M.

plantaris; tendinous anteromedial surface of proximal end fused to common tendon of origin of medial heads of Mm. flexor perforatus digiti III and flexor perforatus digiti II; belly ending approximately halfway down shank.

ORIGIN.--The origin is fleshy and tendinous (anteromedial surface) from the popliteal area immediately distal to the origin of the medial head of M. flexor perforatus digiti IV, extending laterally to the area immediately proximal to the external femoral condyle (medial to the origin of M. gastrocnemius pars externa); the muscle also arises from the proximal end of the posterior part of the articular capsule.

INSERTION.--The slender ossified tendon becomes flexible and pa.s.ses through the ca.n.a.l in the tibial cartilage that lies lateral to the ca.n.a.l for M. flexor perforatus digiti II, then pa.s.ses through a slight groove in the lateral surface of the hypotarsus and becomes ossified again; midway of the tarsometatarsus, the tendon becomes superficial to the tendon of M. flexor digitorum longus and is connected with the latter by an extensive vinculum, which extends from the deep surface and lateral edge of the tendon of M. flexor hallucis longus distally to the superficial surface of the tendon of M. flexor digitorum longus; the tendon continues, unossified and considerably reduced in size, distally medial to the tendon of M. flexor digitorum longus, and pa.s.ses through the flexor groove of the first metatarsal anterolateral (adjacent) to the tendon of M. flexor hallucis brevis, then pa.s.ses deep to the terminal expansion of the latter onto the ventral surface of the hallux; the tendon emerges from under the end of the tendon of M. flexor hallucis brevis and attaches to the ventral surface of the ungual phalanx; a weak dorsal slip attaching to the ventral surface of the distal end of the first phalanx is usually present.

INNERVATION.--A branch of the medial division of the tibial nerve pa.s.ses along the medial edge of the muscle, giving several twigs into it.

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

=_M. Plantaris_=, Figs. 15, 19A

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Elongate and tapering; on posteromedial surface of tibiotarsus; bounded medially by M.

gastrocnemius pars interna and tendon of M. flexor cruris medialis, posteriorly by M. gastrocnemius pars media and medial head of M. flexor perforatus digiti III, posterolaterally by M. flexor hallucis longus; medial to M. flexor digitorum longus; anterolateral surface of proximal end often slightly overlapping and fused to posterior surface of medial end of M. popliteus; belly terminating above middle of shank.

ORIGIN.--The origin is fleshy and tendinous (distal edge only) from an elongate area on the posteromedial surface of the proximal end of the tibiotarsus adjacent to the insertion of M. popliteus.

INSERTION.--The long, slender, ossified tendon extends along the posteromedial aspect of the tibiotarsus and becomes flexible just before attaching to the proximomedial part of the tibial cartilage. The tibial cartilage is a large, mostly cartilaginous pad fitting closely over the posterior surface of the intratarsal joint; the distomedial corner is ossified. This cartilage is perforated by the tendons of several flexor muscles; the distal end of the cartilage attaches to the posteroproximal corner of the tarsometatarsus.

INNERVATION.--A branch of the medial division of the tibial nerve penetrates the lateral surface.

INDIVIDUAL VARIATION.--In one leg, a small bundle of fibers separates from the proximal end of the muscle, forming a short accessory head which attaches, separately from the remainder, to the articular capsule posteroproximal to the main origin; a blood vessel pa.s.ses between the main and accessory heads.

_T. cupido_

INDIVIDUAL VARIATION.--In one leg, a small bundle of fibers arises from the medial collateral ligament. In another leg, the nerve to M.

gastrocnemius pars interna pa.s.ses through a gap in the origin of M.

plantaris rather than distal to its origin.

_P. p. jamesi_