80 U.S. NATIONAL MUSEUM BULLETIN 2 73 



Comparative anatomy: The latissimus dorsi of the howUng mon- 

 key presents a condition intermediate between that of Cehus on the 

 one hand and Ateles on the other. In its mild development, it is 

 reminiscent of the situation in the capuchin monkey; but in the direc- 

 tion of its fibers the resemblance is with Ateles. The number of costal 

 digitations, an average of four for a total of seven specimens (three 

 of Sirena (1871), four mine), is intermediate between Cehus and the 

 spider monkey. Schiick (1913a) reports three specimens of the first 

 genus with three, four, and seven sUps, respectively. The first three 

 digitations of the animal with seven were rather weak. Campbell 

 (1937) found only two in one Cehus capucinus. Schiick (1913a) indi- 

 cates six digitations in one Ateles ater ( = Ateles paniscus). Hill's 

 coverage (1962) of the latissimus in Brachyteles suggests that there 

 might be six in this animal. The situation for Lagothrix is not clear, 

 as the only source about this muscle is Campbell (1937), and he 

 says merely that the highest costal origin for latissimus is the eighth 

 rib. The caudal migration of the latissimus origin toward the iUac 

 blade has not gone as far in Alouatta as in Ateles. It stops on the 

 12th (five 14-rib specimens) or 11th (two 13-rib specimens) rib in 

 the first genus, but in the second genus Schiick (1913a) describes it 

 as taking place by six sHps from ribs 9 to 14. The close association 

 of this muscle with the teres major has been reported also in all the 

 other genera, but only Campbell (1937) has found a true origin for 

 the latissimus from the inferior angle of the scapula. 



M. rhomhoideus (fig. 25): This is a strong muscle found deep to 

 trapezius in the neck and upper thoracic regions. Its undivided and 

 flattened belly occupies the space between the vertebral border of 

 the scapula, the occiput, and the spines of all the cervical and upper 

 four vertebrae. Origin is by fleshy and thick bundles from (1) the 

 medial two-thirds of the lambdoid crest and the protuberantia oc- 

 cipitalis externa, between the origin of m. trapezius superficially and 

 the insertion of the spJenius deeply (fig. 5); (2) the Hgamentum 

 nuchae; and (3) the spines of C 7 to T 4 and the associated ligamenta 

 supraspinaha. In the left side of one male the cranial origin was limited 

 to less than one-fourth of the lambdoid crest adjacent to the pro- 

 tuberance. Occipital and cervical fibers form the thicker part of the 

 muscle, those extending from the cranium to the scapula are nearly 

 vertical, the rest increasingly oblique but never attaining a horizontal 

 direction, even in the thorax. The muscle is thicker near its insertion, 

 which is on the dorsal Up of the vertebral border from the caudal 

 angle up to about the middle of the supraspinous part of the margin 

 (fig. 24). 



A comparison of this muscle with that of Alouatta fusca, as described 

 by Sirena (1871), reveals no difference. According to him, the occipital 



