ABT. 13 BRACHIAL FLEXORS IN PRIMATES HOWELL AND STRAUS 13 



In a chimpanzee dissected by Gronroos (1903), the bicipital slip 

 to the forearm fascia was fleshy, thereby contributing a '' lacertiis 

 carnosus.-' Duvernoy (cited by Sommer) and Sommer (1907) found 

 quite similar arrangements in their gorillas, as did Duckworth 

 (1915) in Lemur. This condition, however, appears to be quite dif- 

 ferent from the arrangement in gibbons. In general, the lacertus 

 fibrosus is much more frequently absent in prosimians, monkeys, and 

 anthropoids than it is in man. 



In man there may be accessory heads to the biceps, usually con- 

 cerned with the caput longum, to the number of three. Very rarely 

 are there this many, but it is not very unusual to find at least one. 

 Such an extra head does not mean an extra muscle, of course, but 

 only that one lieacl of the biceps has more than one attachment at 

 origin. These extra heads may arise in various ways; for example, 

 very frequently from the capsule of the shoulder joint or from the 

 shaft of the humerus itself. 



We were fortunate in finding a condition of the former sort in 

 the chimpanzee that we dissected. Upon the right side the origin 

 of the caput longum had two attachments, one proper and the other 

 from the capsule of the joint, both fusing some 60 mm. below the 

 humeral head. Upon the left side there were two extra attachments 

 to the capsule. 



In one specimen of Aotus (Johns Hopkins Anat. No. 237) we 

 found in the left arm what was apparently a liinneral biceps head. 

 This arose from the medial edge of the bicipital sulcus, immediately 

 adjacent and lateral to the insertion of the coracobrachialis medius, 

 beginning a few millimeters above the distal border of the latissimus 

 dorsi tendon and continuing for a short distance below. This 

 muscle was smaller than either of the two usual biceps heads, both 

 of which had their customary attachments. The exact distal con- 

 nections of this extra muscle could not be ascertained because of the 

 fragile condition of the tissues of tliis specimen. Accessory biceps 

 heads with origin very similar to that occurring in this Aotus appear 

 to be not infrequent in man, as observed by us and others in the 

 dissecting room. Thus among 37 arms (23 negro, 14 white), rep- 

 resenting 20 bodies (12 negro, 8 white), in which this detail was 

 particularly sought, we found an accessory humeral head occuri'ing 

 six times (5 negro, 1 white), and an accessory capsular head once 

 (negro). Testut (1884) has reported the occurrence of a humeral 

 biceps head in 31 out of a total of 299 subjects, all of which were 

 presumably white. Our own figures in this coimection suggest that 

 accessory humeral heads may occur more frequently in negroes than 

 in whites. Naturally, however, our data are as yet too meager for 



