OF DIDELPHYS VIRGINIANA. 



129 



tendon. The plantaris is large ; its tendon forms a third tendo achillis. There is no popli- 

 tsciis. The long flexor of the toes lies upon the fibular, and the long flexor of the great toe 

 upon the tibial, side of the leg. The peroneus longus has two insertions ; the peroneus 

 "tertius" is found as the proper extensor of the little toe. The "short " extensor of the 

 toes, instead of lying upon the dorsum of the foot, comes down from the leg above, as one 

 of the peroneal group, whose tendons pass behind the external malleolus ; one fasciculus of 

 it is left upon the instep, constituting the short extensor of the great toe. In like manner 

 the " short" (" perforatus ") flexor of the toes extends some distance up the leg upon the 

 conjoined tendon of the long flexor, from which it takes origin. A curious arrangement of 

 the Hexing muscles of the great toe occurs. 



Study of the muscles of the leg is facilitated by considering them in four groups : first, 

 the anterior tibial— those that pass over the instep ; second, the fibular— those that pass 

 behind the external malleolus ; third, the superficial posterior tibial— those that pass to the 

 heel; fourth, the deep posterior tibial— those that pass behind the internal malleolus, or 

 rather, over the heel, to the foot, including also the inter- 

 osseus cruris. 



Tibialis anticus {"flexor tarsi tibialis''). — (Fig. 33, h.) 

 By far the largest muscle of this region ; the fleshy part 

 is of a somewhat prismatic shape, and extends along three- 

 fourths of the leg. It arises from the head and upper 

 third of the fibular side of the tibia, and intermuscular 

 septum between itself and the common long digital ex- 

 tensor. Its stout, flattened tendon crosses the instep, just 

 in front of the inner malleolus, bound down by the annu- 

 lar ligament, passes obliquely to the inner side of the 

 foot, there to be inserted into the internal cuneiform bone 

 (not base of first metatarsal). It has the usual action. 



Extensor proi^rius pollicis longus. — (Fig. 33, d.) 

 Deep-seated, and covered by the preceding and following 

 muscle. A long, slender, fusiform belly, arising from the 

 upper half of the tibial aspect of the fibula, somewhat 

 blended with the short digital extensor, changing to a 

 slender, flattened tendon just above the ankle, passing 

 beneath the annular ligament, and thence proceeding 

 very obliquely across the instep to gain the great toe, run 

 along the latter, and be inserted into the base of the dis- 

 tal phalanx. 



Extensor communis digitorum longus. — (Fig. 33, c.) 

 A small muscle, overlying the preceding, arising from the 

 head of the fibula in common with the peroneus brevis. 

 Its muscular part is only two or three inches long ; it rap- 

 idly divides mio four parts, representing as many tendons 

 These pass as one down the leg until they emerge from 

 beneath the annular ligament, when they diverge to the 

 four lesser toes, into the base of the ungual phalanges 



Fig, 33. — Anterior tibial and fibular view of 

 the left leg and foot; natural size, a, vas- 

 tus externus. 



MEM0IB3 BOST. 80C. NAT. HIST. VOL. U. 



83 



