86 U.S. NATIONAL MUSEUM BULLETIN 2 73 



facet of the greater tuberosity (fig. 27). The muscle is apparently 

 the same in the other howlers. 



Nerve supply: The suprascapular nerve. 



Function: It is another stabilizer of the joint and is an abductor 

 and lateral rotator of the arm. 



Comparative anatomy of the intrinsic series. — In none of 

 the animals with which I am comparing AloyxMa does there appear 

 to be any significant deviation from the patterns here described 

 for the muscles of the intrinsic series. Information about them was 

 obtained from Ashton and Oxnard (1963), Campbell (1937), Hill 

 (1962), and Senft (1907) for Ateles; Hill (1962) for Brachyteles; 

 Campbell (1937), Hill (1962), and Robertson (1944) for Lagothrix; 

 Campbell (1937), and Senft (1907) for Cebus. A comment should 

 be added. Ashton and Oxnard (1963) explain that the area of the 

 angle taken up by the origin of the muscle teres major is larger in 

 quadrupeds than in semibrachiators. I observed it to be large in 

 Alouatta (fig. 24). 



Upper Arm Group 



M. triceps brachii (fig. 28) : The strong and large triceps is formed 

 by three well-developed portions. The caput longum arises from 

 the upper half of the axillary border of the scapula (fig. 24) and 

 from the infraspinal fascia that surrounds both teres minor and the 

 infraspinatus. Its origin is thereby extended across the surface of 

 these two muscles to the spina scapulae. Lateral fibers of this head 

 are tendinous and come from as high up as the attachment of the 

 articular capsule on the scapula. The medial fibers are muscular. 

 The long head runs distally covered by m. dorso-epitrochlearis. 

 At about the middle of the arm or above, it joins the lateral head 

 to form a single muscular mass which occupies the entire dorsum 

 of the arm and covers the medial head. In one powerfully built 

 male its components were differentiated into two more or less inde- 

 pendent parts. Fleshy superficial fibers came from the border of 

 the bone and adjacent infraspinal fascia to form a voluminous bundle 

 directed distally. Tendinous and deep fibers with origin near the 

 glenoid labrum had a spiral-like course around the superficial fibers. 

 Both portions joined with the lateral head. The caput laterale arises 

 from the upper half of the lateral border of the humerus where its 

 attachment contributes to form a well-marked deltotricipital crest. 

 Its fibers of origin are a mixture of short tendinous and fleshy ele- 

 ments, some of which expand a bit into the posterior surface of the 

 bone. They reach the surgical neck. This head is directed distally 

 until it meets the long one. As the combined belly approaches the 

 elbow, it forms a broad tendon by means of which insertion is made 



