22 PROCEEDINGS OF THE NATIONAL MUSEUM vol.80 



for calling this longer type of muscle a pars longa, for it is appar- 

 ently strictly homologous with the shorter type. And here lies the 

 ambiguity. It is usually impossible to tell whether an author, using 

 the term coracobrachialis longus, has reference merely to the part 

 of the muscle distal to the musculocutaneous nerve (where this 

 pierces), to that part lying distal to the middle of the humerus 

 (where this position is occupied), or to an entirely separate slip, as 

 hereafter defined. Furthermore, when the coracobrachialis is dis- 

 tally extensive one should exercise great care in dissecting the inser- 

 tion free from a possible epitrochleo-anconeus. Where the statement 

 is made that the former continues quite to the epicondyle we are 

 suspicious that the two have not been properly differentiated — an 

 error very easy to make. 



When the coracobrachialis medius is not pierced by the musculocu- 

 taneous nerve the muscular belly is usually not separable into two 

 distinct parts. If piercing does occur, there may be complete separa- 

 tion or only partial. 



The portion of the coracobrachialis termed pars longa has caused 

 us much perplexity, as explained above, for the reason that it is often 

 impossible to be sure of the exact conditions found by an author. 

 It is certain that frequently nothing was meant but an unusually 

 long pars media, while it seems equally apparent that such authors 

 as Wood and Parsons applied the same term indiscriminately to two 

 different structures. Our attention was focused on this point by 

 finding upon the right side of a chimpanzee a rather slender anoma- 

 lous muscle that arose from the coracoid dorsally adjacent to the 

 short biceps origin, and in a position corresponding to the more 

 usual dorsal border of the coracobrachialis medius. This muscle was 

 superficial to all others but the dorsoepitrochlearis, and maintained 

 this position, by a slender tendon, quite to the entepicondyle, thus 

 passing superficial to the median nerve. Its exact homology we 

 can not state. It is probably a derivative of the primitive coraco- 

 brachialis, but the question whether it is a relic of a muscle invariably 

 present in some remote ancestor, or whether an anomalous variation 

 without particular phylogenetic significance, can not now be an- 

 swered, for the reason that although a precisely similar structure 

 has been reported and figured in widely unrelated mammals, we do 

 not know whether it is invariably present in all individuals of those 

 species.* 



* This superficial portion of tlie coracobrachialis was vei'y probably included in the 

 ground plan of the brachial flexors of tetrapod vertebrates. Thus Humphry (1872) 

 states in regard to the coracobrachialis that " in Amphibians, Reptiles, and Monotremes 

 there is commonly a third segment, an inferior coracobrachial, which extends to the 

 ulnar condyle ; and the brachial artery with the median nerve passes between it and the 

 middle coracobrachial" (p. 158). Judged from its superficial position in respect to the 

 median nerve, this muscle described by Humphry may well be considered as homologous 

 to the superficial coracobrachialis of our chimpanzee. 



