76 U.S. NATIONAL MUSEUM BULLETIN 2 73 



shoulder. In the skull the lambdoid crest and the external occipital 

 protuberance are well developed in adult males. The cranial origin of 

 the trapezius is by fleshy fibers from the medial half of the nuchal crest 

 and the external occipital protuberance in five specimens (fig. 5). In 

 the neck and high thoracic region, it arises from the nuchal ligament, 

 the spine of C 7, the spines of the upper thoracic vertebrae (the dis- 

 tribution in five specimens was down to T 7 in two, to T 8 in two, and 

 down to T 9Mn one), and from the intervening supraspinal ligaments. 

 Most of these fibers are fleshy; only those from the last cervicals and 

 first thoracic are aponeurotic and form with the trapezius of the other 

 side a speculum rhomboideum. The lower thoracic fibers have a short 

 tendinous origin. Occipital and higher cervical bundles pass caudolat- 

 erally to insert on the outer half of the clavicle, the acromioclavicular 

 capsule and upper surface of the acromoin (fig. 24). This attachment 

 and the lower half of the lateral border of the trapezius are covered by 

 the atlantoscapularis anterior as this ends on the acromion and clavicle. 

 Intermediate fibers are transversely oriented toward their insertion on 

 the cranial border of the scapular spine. The distal fascicles of the tra- 

 pezius are directed laterocranially, ending by a short aponeurosis on 

 the medial half of the spine. The muscle is thicker in the cervical than 

 in the thoracic region. According to Sirena (1871), the cranial origin 

 in Mycetes fuscus (=- Alouatta fusca) is only from the medial third of 

 the superior semicircular fine and in the vertebral column it reaches 

 T8. 



Nerve supply: Cranial nerve XI after it receives a communicating 

 branch from C II. 



Function: It elevates the shoulder and, as discussed by Oxnard 

 (1963), plays an important part in bringing the glenoid angle of the 

 scapula upwards. 



Comparative anatomy: From a perusal of the available Hterature 

 (Ashton and Oxnard, 1963; Campbell, 1937; Hill, 1960, 1962; Miller, 

 1932; Sirena, 1871), it becomes apparent that the origin of the tra- 

 pezius along the lambdoid crest is larger in the howler than either the 

 spider, woolly, or capuchin monkeys. Data on Brachyteles (Hill, 1962) 

 suggests a similar extensive origin in this genus. With respect to this 

 character, the howler stands apart from the condition of quadrupeds 

 and the other semibrachiators as described by Ashton and Oxnard 

 (1963), but aligns itself with the last in having a thicker cervical than 

 thoracic part of the trapezius and an insertion for this muscle reaching 

 farther out in the shoulder into the clavicle. I regard the wide occipital 

 origin of the trapezius in Alouatta as perhaps related to the possible 

 role of the muscle in helping to hold the head up against the influence 

 exerted by the presence of the heavy hyolaryngeal apparatus in the 



1 Observation in an additional young adult male. 



