Part 12 (2/2)

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Large; on anterolateral surface of shank; bounded medially by M. gastrocnemius pars interna and posterolaterally by Mm. flexor perforans et perforatus digiti III and flexor perforans et perforatus digiti II; proximal three fourths of posteromedial part (covered by M. gastrocnemius pars interna) aponeurotic and tightly fused to medial surfaces of underlying Mm.

tibialis anticus and extensor digitorum longus; proximal part of fleshy belly somewhat fused to anterior surface of underlying M. tibialis anticus; posterolateral surface strongly fused to aponeurotic medial head of M. flexor perforans et perforatus digiti II and slightly fused to anterolateral edge of M. flexor perforans et perforatus digiti III.

ORIGIN.--The muscle arises by fleshy and tendinous fibers from the edges of the inner and outer cnemial crests; the extreme proximal end arises either fles.h.i.+ly or aponeurotically from the rotular crest between the cnemial crests; the posteromedial edge (aponeurotic except distal one fourth fleshy) arises from the anteromedial intermuscular line.

INSERTION.--The narrow ossified tendon on the superficial surface of the distal part of the fleshy belly extends several mm. beyond the belly where it becomes flexible and divides into two branches. The short, broad posterior branch attaches broadly to the proximolateral corner of the tibial cartilage. The narrow anterior branch pa.s.ses along the lateral surface of the tibiotarsus, through a strong retinaculum immediately proximal to the external condyle, and crosses the lateral surface of the joint, where it is covered by connective tissue nearly as tough as, and continuous with, the retinaculum; the tendon attaches broadly to the lateral edge of the ossified tendon of M. flexor perforatus digiti III a short distance below the hypotarsus.

INNERVATION.--The peroneal nerve sends twigs to the deep surface.

INDIVIDUAL VARIATION.--In both legs of two specimens, the extreme proximal end extends proximal to the rotular crest and attaches fles.h.i.+ly to the superficial surface of the distal end of the patellar tendon.

_T. cupido_

INDIVIDUAL VARIATION.--None of significance.

_P. p. jamesi_

INDIVIDUAL VARIATION.--One leg shows the variation described above for _T. pallidicinctus_.

=_M. Tibialis Anticus_=, Figs. 14, 15, 16, 19E, 20N

_T. pallidicinctus_

GENERAL DESCRIPTION AND RELATIONS.--Thick; on anterior aspect of thigh deep to M. peroneus longus; bounded posteriorly by M. extensor digitorum longus and posterolaterally by Mm. flexor digitorum longus and peroneus brevis; divided into two heads--tibial and femoral; small femoral head adjacent to posterolateral surface of much larger tibial head; two heads joined near midpoint of fleshy part of muscle, forming bipinnate belly (pinnate structure most evident on deep surface); proximal part of femoral head situated between outer cnemial crest and head of fibula; proximal part of anterior surface of tibial head somewhat fused to overlying M. peroneus longus; medial surface fused to aponeurosis of latter.

ORIGIN.--_Tibial head_: This arises by fleshy and tendinous fibers from the edge of the inner cnemial crest, from the rotular crest between the inner and outer cnemial crests, and from the anterior surface, distal edge, and posterior surface of the outer cnemial crest; the attachment may or may not extend onto the superficial surface of the distal part of the patellar tendon; the attachment is adjacent to the origin of the underlying M. extensor digitorum longus. _Femoral head_: This arises by a slender tendon from the notch in the distal end of the external condyle of the femur.

INSERTION.--The slender ossified tendon extends along the anterior surface of the distal end of the tibiotarsus and pa.s.ses through a large, strong, oblique retinaculum (superficial to the supratendinal bridge); the lateral end of the retinaculum attaches to the lateral end of the supratendinal bridge; the medial end attaches immediately proximal to the medial end of the bridge. The tendon widens and becomes flexible as it pa.s.ses across the anterior surface of the intratarsal joint, then narrows and attaches to the tubercle on the anterior surface of the proximal part of the tarsometatarsus between Mm. extensor hallucis longus and extensor brevis digiti IV. The distalmost bundle of tendinous fibers does not attach to the tubercle, but extends distally along the anterior surface of the tarsometatarsus and attaches to the latter a few mm. distal to the tubercle, forming an accessory insertion.

A part of the peroneal nerve pa.s.ses between the main and accessory insertions.

INNERVATION.--A variable number of branches of the peroneal nerve penetrate the lateral surface of the femoral head; a variable number of branches of the same division pa.s.s deep to the femoral head and enter the posterior edge of the tibial head.

INDIVIDUAL VARIATION.--- In one leg, the accessory insertion is absent.

_T. cupido_

INDIVIDUAL VARIATION.--None of significance.

_P. p. jamesi_

DIFFERENCES FROM TYPICAL _T. pallidicinctus_.--The origin of the tibial head does not extend onto the patellar tendon.

INDIVIDUAL VARIATION.--The accessory insertion is absent in one leg.

=_M. Extensor Digitorum Longus_=, Figs. 15, 17

<script>