Part 10 (2/2)

_P. p. jamesi_

INDIVIDUAL VARIATION.--None of significance.

=_M. Flexor Perforans et Perforatus Digiti III_=, Figs. 12, 14

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Thick, bipinnate; on lateral surface of proximal part of shank between two heads of M. flexor perforans et perforatus digiti II; bounded anteriorly by M. peroneus longus; anterior surface fused with tendinous anterior head of M. flexor perforans et perforatus digiti II; anterolateral edge somewhat fused to posterior edge of M. peroneus longus superficial to latter tendon; posterior surface fused to posterior head of M. flexor perforans et perforatus digiti II; distal part of belly covered by common belly of latter muscle; posteromedial edge fused to underlying lateral head of M. flexor perforatus digiti IV; anteromedial edge usually somewhat fused to underlying M. flexor digitorum longus.

ORIGIN.--The origin is fleshy and tendinous from the edge of the outer cnemial crest and fleshy from the superficial surface of the distolateral part of the patellar tendon; the posteroproximal corner arises tendinously from the femorofibular fascia.

INSERTION.--The belly narrows abruptly, terminating approximately at the middle of the shank; the slender ossified tendon extends posterodistally along the shank, becoming flexible before pa.s.sing posterior to the tibial cartilage deep to the tendon of M. gastrocnemius, medial to the tendon of M. flexor perforatus digiti IV, and superficial to the medial half of the tendon of M. flexor perforatus digiti III; a thin sheet of connective tissue covers the tendon and attaches by its edges to the underlying tendon of M. flexor perforatus digiti III (thus the latter tendon forms a sheath for the tendon of M. flexor perforans et perforatus digiti II); the tendon is ossified for most of the length of the tarsometatarsus; at midlength of the latter, the tendon lies between the tendons of Mm. flexor perforatus digiti IV and flexor perforatus digiti III; near the distal end of the tarsometatarsus, the tendon becomes lateral and then deep to the tendon of M. flexor perforatus digiti III and is connected by a vinculum to the latter (which see). The tendon enters the ventral surface of digiti III between the tendons of Mm. flexor perforatus digiti III and flexor digitorum longus; after sending a dorsal slip (lateral to the tendon of M. flexor digitorum longus) to the subarticular cartilage ventral to the first interphalangeal joint, the tendon divides into two branches, between which emerges the tendon of M. flexor digitorum longus; the lateral branch attaches to the subarticular cartilage of the second interphalangeal joint and to the lateral surface of the distal end of the second phalanx; the medial branch has similar attachments on the medial side of the digit.

INNERVATION.--A branch of the lateral division of the tibial nerve pa.s.ses deep to the posterior head of M. flexor perforans et perforatus digiti II and enters the posteromedial edge of M. flexor perforans et perforatus digiti III.

INDIVIDUAL VARIATION.--In both legs of one specimen, the part arising from the femorofibular fascia appears as a distinct but short accessory head. There is no significant individual variation in _T. cupido_ or _P.

p. jamesi_.

=_M. Flexor Perforatus Digiti IV_=, Figs. 14, 16

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--On posterolateral aspect of shank deep to M. gastrocnemius pars externa; bounded medially by medial head of M. flexor perforatus digiti III, anterolaterally by posterior head of M. flexor perforans et perforatus digiti II, and anteriorly by M. flexor digitorum longus; divided into three heads--medial (largest), lateral, and anterolateral (smallest); tendon of insertion of M. extensor iliofibularis pa.s.sing between medial and lateral heads; proximal and anteroproximal parts of _lateral head_ an extremely thin, flat tendon; anterodistal part of tendon fused to lateral surface of fleshy part of underlying lateral head of M. flexor perforatus digiti II; proximal part of tendon fused indistinguishably to tendinous part of underlying lateral head of M. flexor perforatus digiti II; fleshy part of _anterolateral head_ anterodistal to lateral head; proximal part of former a long slender tendon anterior to lateral head; anterior surface of anterolateral head (both fleshy and tendinous parts) fused to tendon of anterolateral head of M. flexor perforatus digiti III; deep surface fused to underlying anterolateral head (fleshy) of M. flexor perforatus digiti II; common tendon of anterolateral heads of M. flexor perforatus digiti IV and M. flexor perforatus digiti III pa.s.sing medial to tendon of insertion of M. extensor iliofibularis, to peroneal nerve, and to fibular arm of guide loop for M. extensor iliofibularis; tendon of M.

ambiens inserting on anterolateral surface of this common tendon; _medial head_ entirely fleshy; medial surface fused to medial head of M.

flexor perforatus digiti III; deep surface fused to medial edge of underlying medial head of M. flexor perforatus digiti II; medial and lateral heads joined, forming bipinnate belly (pinnate structure most evident on deep surface); anterolateral head joined to distolateral part of belly.

ORIGIN.--The _medial head_ attaches fles.h.i.+ly to the proximal part of the popliteal area proximal (adjacent) to the origin of M. flexor hallucis longus and distolateral to the distal end of the origin of M.

femorocruralis; the attachment extends laterally onto the posterolateral surface of the femur proximal (adjacent) to the common attachment of M.

gastrocnemius pars externa and the distal arm of the guide loop for M.

extensor iliofibularis; the medial edge of the origin is fused with part of the tendinous origin of the medial head of M. flexor perforatus digiti III.

The broad flat common tendon of the _lateral head_ and the lateral head of M. flexor perforatus digiti II fuses to the superficial surface of the fibular arm of the guide loop for M. extensor iliofibularis and contributes to the femorofibular fascia; consequently the ultimate origin would be the external femoral condyle and the head of the fibula.

The slender common tendon of the _anterolateral head_ and the anterolateral heads of Mm. flexor perforatus digiti II and flexor perforatus digiti III pa.s.ses deep to the insertional tendon of M.

extensor iliofibularis and to the fibular arm of the guide loop for the latter muscle (to which it partly fuses); the tendon attaches to a narrow line on the head of the fibula adjacent to the attachment of the fibular arm of the guide loop and to the deep part of the femorofibular fascia.

INSERTION.--The slender ossified tendon becomes flexible before it pa.s.ses posterior to the tibial cartilage deep to the tendon of M.

gastrocnemius, lateral to the tendon of M. flexor perforans et perforatus digiti III, and superficial to the lateral half of the tendon of M. flexor perforatus digiti III; a thin sheet of connective tissue covers the tendon and attaches by its edges to the underlying tendon of M. flexor perforatus digiti III (thus the latter tendon forms a sheath for the tendon of M. flexor perforatus digiti IV; this sheath is separate from a similar sheath surrounding the tendon of M. flexor perforans et perforatus digiti III); the tendon is again ossified where it pa.s.ses along the posterolateral surface of the tarsometatarsus posterolateral to the tendon of M. flexor perforans et perforatus digiti III; near the distal end of the tarsometatarsus the tendon becomes flexible and expands greatly in width and thickness, and sends a small slip dorsally, medial to the underlying tendons, that attaches to the subarticular cartilage ventral to the trochlea for digit IV; sometimes this slip is continuous with the retinaculum ventral to the tendon at the level of the proximal end of the digit. Several more or less distinct sheets of tough connective tissue lie ventral to all of the flexor tendons at the level of the trochleae and the proximal end of the digits, holding them in place. The tendon narrows as it pa.s.ses onto the ventral surface of digit IV and soon divides into three branches; the tendon of M. flexor digitorum longus emerges between the medial and middle branches. The lateral branch attaches to the subarticular cartilage ventral to the first interphalangeal joint and is also bound by connective tissue to the ventrolateral surface of the first phalanx.

A dorsal slip arises at the point of divergence of the lateral and middle branches and attaches to the subarticular cartilage of the first interphalangeal joint. The middle branch attaches to the subarticular cartilage of the second joint. The medial branch, after sending dorsal slips to each of the first two subarticular cartilages, attaches to the subarticular cartilage of the third interphalangeal joint.

INNERVATION.--The posterior division of the tibial nerve sends a branch into the posterior edge of the medial head, then pa.s.ses between the latter and the medial head of M. flexor perforatus digiti III; as it extends distally it gives off twigs to the medial surface of the medial head, to the deep surface of the lateral head, and to the deep surface of the anterolateral head.

INDIVIDUAL VARIATION.--In one leg, an additional branch arises from the tibial nerve at the level of origin of the posterior division and enters the posterior surface of the medial head; a twig from this branch anastomoses with the first twig of the posterior division to the same head; a branch of the medial division joins the posterior division distal to the origin of the twigs to the medial head but proximal to the origin of the twigs to the other heads.

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