MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 107 



Grand's observations (1967) in Alouatta caraya attribute an extension 

 of 70 percent of the radial shaft to the insertion of this muscle. 



Nerve supply: It receives two branches from the medial nerve, 

 one proximally, the other distally. 



Function: I assume from the development of this muscle that 

 pronation is an important function in the forearm of this animal. 



M. fiexor- carpi radialis: This muscle is medial to the former and 

 lies over the lateral border of the flexor digitorum superficialis (fig. 

 32). It is ventraUy flattened with a proximal muscular and a distal 

 tendinous part. It arises by mixed tendinous and fleshy fibers from 

 the ventral and intermediate portion of the ulnar epicondyle, near 

 fibers of the superficial head of the flexor digitorum superficiaUs on 

 whose deep and tendinous side many fibers of the flexor carpi radialis 

 take firm origin (fig. 27). The muscle runs distally across the ventral 

 aspect of the limb toward the radial side of the carpus. It narrows 

 down to a strong tendon on reaching the distal third of the forearm. 

 This tendon enters a separate path in the flexor retinaculum and 

 pierces the origin of m. abductor pollicis brevis. In the central manual 

 compartment the tendon passes along the medial side of the trapezium 

 crest and crosses the carpometacarpal joint of the second digit to 

 insertion on the palmar base of metacarpale II. On the right side of 

 one male the tendon of m. flexor carpi radialis provides a strong 

 tendinous contribution to that of the palmaris longus. 



The insertion of this muscle in Alouatta fusca (Sirena, 1871) and 

 Alouatta caraya (Grand, 1967) is said to be on both the second and 

 third metacarpal. 



Nerve supply: The medial nerve gives off a branch which enters 

 the muscle proximally. 



Function: Flexes the hand on the forearm. 



SUPERFICIAL SERIES, INTERMEDIATE DIVISION 



M. flexor digitorum superficialis (fig. 32) : It is found superficially 

 in the ventral aspect of the forearm between the palmaris longus 

 and flexor carpi radialis which conceal its medial and lateral borders, 

 respectively. It is formed by two entirely separate parts with different 

 origins and insertions. (1) A caput superficiale arises from the medial 

 epicondyle between flexor carpi radialis and the pronator teres above 



Figure 32. — Ventral view of the forearm and hand (1, m. supinator; 2, m. pronator teres, 

 radial ending; 3, m. flexor digitorum profundus, caput radiale; 4, tendon of m. flexor carpi 

 radialis; 5, m. flexor pollicis brevis; 6, m. abductor pollicis brevis; 7, m. flexor digiti 

 quint ( = digiti minimi of N.A.); 8, m. abductor digiti quinti (= abductor digiti minimi 

 of N.A.); 9, m. flexor carpi ulnaris; 10, m. flexor digitorum profundus, caput ulnare; 

 11, m. flexor digitorum superficialis, caput profundum; 12, m. palmaris longus; 13, m. 

 flexor digitorum superficialis, caput superficiale; 14, m. flexor carpi radialis; IS, m. pronator 

 teres. 



