MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 103 



(Campbell, 1937; Hill, 1960) and the minor arises only from the 

 sternum (Campbell, 1937; Hill, 1960). 



INTRINSIC SERIES 



Of the two muscles included here by Straus (unpublished), only 

 the coracobrachialis will be studied under this heading. The biceps 

 brachii, caput breve is considered with the next group because of 

 topographic and functional reasons. 



M. coracobrachialis: The muscle is divided into two parts and 

 extends from the short bicipital head to the humerus. (1) Pars profunda 

 is formed by fleshy fibers which split off the deep surface of the caput 

 breve tendon very near the coracoid process. Its short belly is directed 

 toward the surgical neck of the humerus where its ending shows 

 some variability. In two males, after passing in front of the subscapular 

 tendon, the pars profunda turns backward around its caudal margin, 

 gaining a fleshy attachment to the surgical neck between the but- 

 tresses of the head and lesser tuberosity. In another male and in the 

 female the insertion occurs on the lesser tuberosity between the 

 attachments of m. pectoralis abdominalis in front and the powerful 

 subscapular tendon behind (fig. 27). In the first case the coracobrachi- 

 alis ending projects a little into the origin of m. vastus lateralis, in 

 the second its more distal fibers are covered by the highest ones of 

 the latissimus. (2) Pars media arises also by fleshy fibers from the 

 deep aspect of the short tendon, a little beyond the origin of the 

 profunda fibers. Its fusiform belly follows the same direction as the 

 caput breve bicipitalis, passes in front of the latissimus tendon and 

 has a fleshy ending just distal to and a bit in front of the attachment 

 of that tendon (fig. 27) . I found the musculocutaneous nerve invariably 

 passing between the two parts of the muscle. 



Sirena (1871) did not note the division of the muscle into partes 

 profunda and media. Howell and Straus (1931) did not find the pars 

 profunda in Alouatta but Campbell (1937) speaks of both portions as 

 present in aU the animals he studied, including one Alouatta palliata. 



Nerve supply: The pars profunda receives one or more small 

 branches from the musculocutaneous before this nerve passes through 

 the two heads. The caput media is supplied by a more distal twig 

 from the same nerve. In the illustrated diagram of the brachial 

 plexus these nerves are shown coming directly from the lateral cord 

 (fig. 26). 



Function: Flexor of the arm. 



Comparative anatomy: Howell and Straus (1931) found a slender 

 pars profunda in Ateles and in only one out of two specimens of Cebus. 

 Hill (1962) reports the presence of both parts in the spider monkey, 

 but only the pars media in Brachyteles. Hill (1962) and Robertson 



