ART. 13 BRACHIAL FLEXOES IN PRIMATES HOWELL. AND STRAUS 11 



represents a portion of the original biceps element, from which was 

 later derived that element (caput longum) almost invariably encoun- 

 tered in mammals, from the glenoid border to the forearm. Simi- 

 larly it must be conceded, for convenience at least, that those elements 

 passing from the coracoid to any part of the humerus represent the 

 coracobrachialis. 



Representing the third primitive flexor of the brachium is the 

 brachialis, the more distal of the two short flexors. Although the 

 mas-s may be either longitudinally divisible or single, and the origin 

 may migrate up or down the humerus, it is always composed of 

 fibers arising from the humeral shaft and inserting upon the ulna. 

 In its idealistically primitive form its plan probably corfsistcd of an 

 origin from the entire humeral shaft, and insertion upon both anti- 

 brachiai bones. 



M. hiceps hrachii. — As the long head of the biceps is absent in all 

 vertebrates below the reptiles, we may presume that it was a later 

 development from the short or coracoid head. This being the case, 

 it is somewhat unexpected to find that in mammals the long head is 

 by far the more conservative, apparently being always present. It 

 arises from the bicipital tuberosity, or tuberositas supraglenoidalis, 

 of the scapula at the lateral base of the coracoid process. It passes 

 ov^er the head of the humerus, either partially or com.pletely deep to 

 the shoulder capsule, and through the bicipital groove, or sulcus in- 

 tertubercularis, between the greater and lesser tuberosities of the 

 humerus. This groove is shallow or deep. The muscle ends invari- 

 ably in a tendon, which inserts upon the bicipital or radial tuberosity 

 of the radius, or the adjoining part of the ulna, or both. The inser- 

 tion has fair but not complete group constancy. In marsupials the 

 short head always goes to radius, the long head to ulna (Leche, 1900). 

 Among primates, on the other hand, it is the rule for both heads to 

 have a common tendon of insertion upon the radius alone. In many 

 rodents there is but a single head, and where this is the case the 

 tendency seems to be for the insertion to be ulnar; but in the seal and 

 sea lion the single head has the radial attachment. At any rate the 

 attachment of this head is always firmly upon the bone. 



Among primates, apparently only the lorises {Nycticelus, Loris, 

 and Stenops) normallj^ have but a single biceps head, of the long 

 variety (Owen, 1868; Murie and Mivart, 1872; Zuckerkandl, 1898; 

 Howell and Straus), yet even in these animals a short or coracoid 

 head may occasionally be present (see Murie and Mivart, 1872). 



Where a second head is present this usually arises from the cora- 

 coid process and constitutes the regular caput breve. In reality 

 there may be considered to be a common tendinous origin of this 

 head and the coracobrachialis, from the superficial aspect of which 



