160 U.S. NATIONAL MUSEUM BULLETIN 2 73 



Nerve supply: The medial plantar nerve sends a branch to the 

 muscle while in the calcaneal canal. 



Function: Abduction of the first toe. 



M. flexor digitorum brevis: The i)erforated flexor lies deep to the 

 plantar aponeurosis in the central foot compartment, where it covers 

 the two long flexor tendons. 



The caput superficiale is well developed and forms a flat, distally 

 tapering belly whose fleshy fibers arise from the calcaneal tubercle. In 

 the female some fascicles come from the proximal part of the plantar 

 aponeurosis. The origin is covered by that of m. abductor hallucis. In 

 the middle of the metatarsus the head gives rise to two (one male, 

 fig. 49d) or three tendons (two males, fig. 49a, b; one female, fig. 49c). 

 The caput i)rofundum is separated from the superficialis by the 

 lateral plantar nerve and accompanying vessels. Its fleshy fibers arise 

 from the plantar surface of the flexor tibialis tendon and by a few 

 distal slips from that of the fibularis. They are continuous without in- 

 terruption with the muscular fibers of the tibial flexor as described 

 above. This head divides into four bellies from which individual 

 tendons proceed toward the second to fifth toes (two males, fig. 49b, 

 d; one female, fig. 49c), except in one male (fig. 49a), where only two 

 bellies are formed. These supply the perforated tendons to toes III and 

 IV, that for the fifth coming as a direct branch of the long flexor tendon 

 to toe V. Typically, a perforated tendon splits distal to the base of the 

 first phalanx, the two resulting fascicles inserting on the margins 

 of the corresponding second phalanx. They are joined by vincula 

 brevia to that bone. 



The pattern of the muscle in Alouatta fusca (Sirena 1871) differs 

 from any of those described here. In this species the caput super- 

 ficiale forms the short tendons to toes II and III, the profundum those 

 for the fourth and fifth plus a contribution to the tendon of the third. 

 Sawalischin (1911) found the superficial head of a Mycetes (= Alouatta 

 giving a small tendon to toe II and a large one to III; the deep head 

 provided a more robust contribution to the tendon of II, a fine one to 

 that of III, and the single tendons for IV and V. Hill's (1962) de- 

 scription of the muscle resembles that of Sawalischin, except that 

 the third toe tendon received no apparent contribution from the deep 

 head. 



Nerve supply: A branch of the medial plantar nerve enters the 

 superficial head on its plantar aspect in approximately the middle of 

 the belly, supplies it, and then innervates the deep one. 



Function: Flexion of the toes at the proximal interphalaugeal 

 joints. 



M. abductor digiti quinti { = abductor digiti minimi oj' N.A.): This 

 nuiscle is not as well developed as the abductor of the hallux and was 



