AitT. 13 BRACHIAL FLEXORS IN PRIMATES HOWELL AND STRAUS 25 



We found some variation in the exact manner in which the cora- 

 cobrachialis is innervated. In some animals (as Galago and Nycti- 

 cehus) the entire muscle (both profundus and medius) was served by 

 branches directly from the musculocutaneous nerve. Sometimes, 

 however, the nerve to the coracobrachialis profundus was derived not 

 from the musculocutaneous nerve proper but from another portion 

 of the plexus. Such an arrangement occurred in Papio^ in Tarsius 

 {pMlippinsnsisf)^^ and in Aotus (No. 237). In both the Papio and 

 the Tarsius the profundus was innervated by a branch from the 

 lateral head of the median nerve just below the point where the mus- 

 culocutaneous nerve diverged from the lateral cord of the plexus. 

 According to Kohlbrligge (1897) both Westiing and Hofer likewise 

 found the coracobrachialis innervated by the median nerve in their 

 orangs. This does not indicate a heterotopic innervation from the 

 median nerve proper, but implies that certain fibers normally car- 

 ried in the trunk of the musculocutaneous may at times continue for a 

 space with those of the median. In the Aotus^ on the other hand, the 

 profundus received a nerve branch from the plexus proximal to the 

 origin of the musculocutaneous nerve. It is, of course, well knowm 

 that in man the nerve to the coracobrachialis frequently does not 

 issue from the musculocutaneous nerve, but instead has an independ- 

 ent origin from the seventh (or seventh and sixth) cervical nerves. 

 This indicates that these nerve fibers, usually carried with the mus- 

 culocutaneous, at times become independent proximal to the forma- 

 tion of that trunk. This is just the opposite to the arrangement in 

 Papio and Tarsius {philippinensisf) . Bolk (1902) also found a 

 separate nerve for the coracobrachialis medius in the orang-utan and 

 Midas rosalia, and for the coracobrachialis profundus in Cynoceph- 

 alus habuin. In the specimen of spider monkey (Ateles geoffroyl) 

 we found that at the upper third of the brachium the median nerve 

 sent a branch to join the terminal division of the musculocutaneous 

 nerve, which then ended in the substance of the brachialis muscle. 

 At the same point was the sole origin, from the median, of the lateral 

 antibrachiai cutaneous nerve. In this case, therefore, the muscu- 

 locutaneous nerve carried no cutaneous fibers. This arrangement 

 may possibly be the rule for the spider monkey, for Bolk likewise 

 found in Ateles helsehuth that the n. cutaneus antibrachii lateralis 

 arose only from the median nerve, the musculocutaneous nerve ter- 

 minating in the brachialis muscle. A branch from the median to 

 musculocutaneous was also encountered in the baboon {Papio), the 

 langur (Pygafhrix), and the guenon {Lasiopyga). In these ani- 

 mals the anastomosis took place in the distal third of the upper arm. 



= In Tarsius saltator the coracobrachialis profundus was innervated by a branch 

 issuing directly from the trunk of the musculocutaneous nerve. 



