ART. 13 BRACHIAL FLEXORS IN PRIMATES HOWELL AND STRAUS 17 



Despite the differences in these theories there seems to be general 

 agreement that the supraglenoid origin of the long head is a sec- 

 ondary occurrence, xls stated earlier in this paper, we are personally 

 inclined to favor the theory that derives both bicei^s heads from a 

 primitive coraco-antibrachial flexor, the outer portion of which has 

 migrated to the supraglenoid border, while the inner has retained 

 its coracoid origin, possibly strengthened by additional fibers from 

 the primitive coracobrachialis. 



Attention must be given to tiie possible significance of the lacertus 

 fibrosus. Gronroos regarded this as a vestigial structure, the remains 

 of the fleshy ulnar extension of the supposedly primitive caput 

 tuberculoseptale of the gibbons. The frequent absence of the lacertus 

 fibrosus in the three great apes, together with the fact that super- 

 numerary biceps heads apparently occur less frequently in these 

 animals than in man, led him to the conclusion that the biceps muscle 

 in all three anthropoids is more specialized than in man. It seems 

 that he was probably correct in asserting that retention of the lacertus 

 is more primitive than is its loss. There is, however, no reason for 

 regarding the condition in the gibbons as other than an extreme 

 specialization. The lacertus possibly represents a portion of the 

 original ulnar insertion of the primitive coraco-antibrachial flexor. 

 At least the conditions in our Galago are extremely suggestive of 

 such an interpretation. 



M. coracohrachialis. — In man, where ordinaril,y there occurs but 

 one well-defined coracobrachialis element, inserting upon the middle 

 of the humeral shaft, there is no difficulty met with, or at least any 

 question that may occur does not greatly worry the human anato- 

 mist. But in many other mammals the conditions that occur in this 

 muscle have been extremely puzzling, which is largely attributable 

 to the loose manner in which the term " longus " has been used for an 

 occasionally present distal extension. 



Comparative anatomists usually follow Wood (1867) when differ- 

 entiating parts of the coracobrachialis. This authority recognized a 

 pars brevis, or coracocapsularis, arising from the coracoid and insert- 

 ing upon the neck of the humerus above the tendon of the latissimus 

 dorsi, a pars media or propria, inserting below the latissimus, and a 

 pars longa. In regard to the last his statements were at times 

 ambiguous, and he seems to have used the term indiscriminately to 

 designate both the distal part of the pars media, when this extended 

 down the shaft to a marked extent, and another structure, totally 

 distinct in conformation. The latter has probably been found by few 

 anatomists, and by the same token it is probably poorly understood, 

 so that subsequent writers have readily fallen in with the same 

 ambiguity of Wood's paper. 



