MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 145 



Nerve supply: The muscle receives a branch from the deep 

 peroneal nerve. 



Function: It extends the two distal phalanges and according to 

 Strode (1937) contributes to spreading of the toes. 



Pedal Group 



M. extensor digitorum brevis et hallucis: Its origin is from the 

 sinus tarsi where the anchorage of the retinaculum for the extensor 

 digitorum longus divides it into a portion for the hallux and one for 

 the other toes (fig. 45). 



M. extensor digitorum brevis arises by fleshy fibers from the 

 laterodorsal aspect of the greater calcaneal process. These group into 

 four flat bipennate bellies which pass over the metatarsus deep to the 

 tendons of the extensor digitorum longus. Each develops a central 

 tendon which receives the insertion of the muscular fascicles. The 

 tendons reach the metatarsophalangeal joints where the first two end 

 by joining the deep aspect of both dorsal extensor expansions to the 

 second toe, the first on the tibial side, the second on the fibular. The 

 third and fourth tendons blend with the extensor expansion to the 

 fibular side of the third and fourth metatarsophalangeal articulations. 

 M. extensor hallucis brevis originates from the dorsal surface of 

 the greater calcaneal process where the insertion of the retinaculum 

 already mentioned separates it from the bundles destined for the 

 other toes. A flat belly is formed, larger than any of the pre\ious 

 part. A long tendon appears at its distal end, runs deep to that of 

 the extensor hallucis longus and expands over the dorsum of the first 

 metatarsophalangeal joint where it ends. Sirena (1871) does not re- 

 port two tendons to the dorsal extensor expansion of the second 

 metatarsophalangeal joint. 



Nerve supply: The deep peroneal nerve. 



Function: It extends the hallux and the next three toes at the 

 metatarsophalangeal joints. It spreads toes II, III, and IV. 



Comparative anatomy of the cruropedal and pedal groups. — 

 The cruropedal muscles of Ateles, Brachyteles, and Lagothrix, all of 

 which are covered to a certain extent by Hill (1962), can be easily 

 matched to those of Alouatta. The findings of Ruge (1878a) in Ateles 

 and CebiLs also accord in general with my data on the howler. The 

 extensor digitorum longus of the wooUy monkey is said to supply 

 tendons only for toes III, IV, and V (Hill, 1962). The two tendons of 

 m. tibialis anterior in the woolly spider monkey are inserted, respec- 

 tively, on the navicular and on the base of metatarsale I (Hill, 1962). 

 This animal has only three bellies destined for toes II, III, and IV 

 from the extensor di.itorum brevis and its m. peroneus digiti quinti 

 is described by Hill (1962) as just a small tendon given off from that 



