104 U.S. NATIONAL MUSEUM BULLETIN 2 73 



(1944) indicate that Lagothrix has both parts. It appears as though 

 Senft (1907) did not find a pars profunda in either Cebus or Ateles. 



Upper Arm Group 



M. biceps brachii (fig. 31) : It arises by two heads, a short and 

 long, which in the ventral aspect of the arm form a pair of round and 

 elongated muscular masses. The caput longum originates from the 

 supraglenoid impression by a long and strong tendon which travels 

 ventrolaterally through the capsule of the scapulohimieral joint. It 

 then turns downward to enter the broadened and shallow bicipital 

 groove where it is proximally covered by the transverse humeral 

 Ugament. A Httle beyond the surgical neck of the humerus the tendon 

 gives rise to the muscular fibers of the lateral belly of the biceps. An 

 equally strong tendon from the tip of the coracoid process gives rise 

 to the caput breve. Its muscular bundles begin in front of the surgical 

 neck of the humerus and form the medial belly. The two are closely 

 apposed along the midline of the arm until at about the junction of 

 the middle and distal thirds of the humerus thej'^ combine into a 

 single and common mass. This enters the antecubital fossa between 

 the brachialis laterally and the forearm flexors medially. It becomes 

 now a flat and broad tendon inserted on the radial tuberosity (fig. 27). 

 A true aponeurosis of the biceps brachii is not present, but in the 

 antecubital fossa the muscle is connected to the mass of the forearm 

 flexors by the antebrachial fascia reinforced by some fibrous elements. 



Sirena (1871) explains that the muscle in Alouatta fusca is like that 

 of man. My findings agree with those of Campbell (1937) in the Central 

 American howler. 



Nerve supply: Small branches of the musculocutaneous nerve 

 enter each beUy in the proximal part of the arm. 



Function: It elevates the arm and also flexes and supinates the 

 forearm. 



M. brachialis: It is a broad muscle over the anterior aspect of the 

 humerus (fig. 31) and covered by the biceps. The musculocutaneous 

 nerve runs distally between these two muscles. Brachialis originates 

 from the entire lateral and medial surfaces of the lower three-fourths 

 of the humeral shaft (fig. 27). Its fibers ascend proximally a little 

 higher up on the lateral side where they intervene between the inser- 

 tions of m. deltoideus and the lateral intermuscular septum. The 

 brachialis becomes laterally compressed as it approaches the elbow at 

 the same time that it lies between the biceps and the brachioradialis. 

 Its sheath is joined to the last muscle by abundant fibrous connective 

 tissue. M. brachialis forms a robust tendon which, after running be- 

 tween that of the biceps and the capsular ligaments of the elbow, 

 ends just distal to the coronoid process (fig. 27). Sirena (1871) offers 

 no particular comment about this muscle in his study. 



