142 U.S. NATIONAL, MUSEUM BULLETIN 2 73 



separate this muscle from the other two peronei. Its belly narrows 

 down to a small tendon which accompanies that of the peroneus 

 brevis around the lateral malleolus, through the compartment for 

 that muscle in the inferior peroneal retinaculum and then passes 

 under the arch formed by the unequal splitting of the brevis tendon 

 (fig. 44). The peroneus digiti quinti runs now superficially along the 

 fibular side of the fifth metatarsal until it ends on the peroneal side 

 of the dorsal extension expansion to this toe (fig. 45). The peroneus 

 digiti quinti in Alouatta jusca (Sirena, 1871) is hke that of the seni- 

 culus species. Its ending in Mycetes niger {= Alouatta palliata) is 

 said (Frets, 1911) to be both on the peroneal process of toe V and 

 the corresponding dorsal expansion. In my opinion. Frets (1911) 

 overlooked the fact that the insertion on the fifth metatarsal belongs 

 to m. peroneus brevis. 



Nerve supply: A branch of the common peroneal nerve. 



Function: Abductor of the fifth toe and the foot. 



ANTERIOR DIVISION 



M. tihialis anterior: It is the best developed of all three muscles 

 in the anterior crural compartment. Fleshy fibers arise from (1) the 

 upper half of the lateral tibial surface between the tibial crest and 

 the weakly defined attachment of the interosseous membrane (fig. 38), 

 (2) the tendinous septum which appears in the upper third of the 

 leg between this muscle and the extensor digitorum longus, (3) the 

 crural fascia, and (4) the interosseous membrane. Proximally, they 

 reach the front of the lateral tibial condyle and distally, half way 

 to the ankle, the elongated belly divides into two heads; one is con- 

 tinued over the lower third of the tibia as a smaller anterolateral 

 and the other as a larger posteromedial round tendon. Both pass 

 under the superior extensor retinaculum covering that of the extensor 

 hallucis longus to reach the tibial border of the foot where they 

 cross over the scaphoid and the medial cuneiform (fig. 45). The 

 anterolateral tendon ends on the tibial side and plantar aspect of 

 the base of metatarsale I. The posteromedial expands as it roUs over 

 the cuneiform partially covered by the other portion of the tibialis 

 anterior. Its insertion is on the plantar surface of that cuneiform 

 and base of the first metatarsal. Other studies of this muscle in the 

 howler monkey reveal no difference (see Sirena, 1871). 



Nerve supply: The deep peroneal nerve. 



Function: It produces dorsiflexion of the foot. By the antero- 

 lateral tendon it abducts the hallux and as a whole the muscle inverts 

 the foot. 



M. extensor hallucis longus: With origin from (1) a narrow area of 

 the upper third of the interosseous membrane and (2) the septal 



