46 U.S. NATIONAL MUSEUM BULLETIN 2 73 



m. spleniiis cervicis. In Lagothrix, the muscle arises from the pro- 

 tiiberantia occipitaHs externa down to the spine of T 1 or T 2, and in 

 the woolly spider monkey its origin is from the spinous process of 

 the axis to that of T 2 (Hill, 1962). No information seems to be avail- 

 able ior Ateles in this respect. In Cebus, the origin is said to be from the 

 first four ribs (Hill, 1960). Meckel (1828) describes a splenius cervicis 

 in both S. capucina (= Cebus nigrivittatus) and S. paniscus (=Ateles 

 paniscus). In the first case the muscle is not separated from the rest 

 of the splenius and is inserted on the atlas. The separation is complete 

 in the spider and its attachment on the first two cervical vertebrae. 

 Hill (1960), nevertheless, asserts that the splenius colli is not differen- 

 tiated in Cebus. His statements may perhaps be interpreted as a 

 generalization for all cebids because it is presented in his account on 

 the myology of these animals and there is no explanation restricting 

 this detail to any of the genera in particular. The suboccipital muscles 

 of the woolly spider monkey as described by Hill (1962) resemble those 

 of Alouatta. 



Hypoaxial Musculature 



The hypoaxial musculature has been arranged by Straus (unpub- 

 lished) into five groups. 



Lateral Group 



It includes several muscles of which the scalenes will be the first I 

 shall deal with. The complex scalene mass extends at each side of the 

 cervical spine from the transverse processes of the corresponding 

 vertebrae to the upper ribs. Kohlbrugge (1897) explained that its 

 subdivision in anterior, medius, and posterior as it was proposed in 

 human anatomy by Gegenbaur is not applicable for comparative 

 purposes. Howell and Straus (1933) noted that the three scalene 

 muscles in the macaque form a rather complex group whose compo- 

 nents cannot be homologized with those of man. No attempt is made 

 in the case of the howler to imply homologies with the three muscles 

 in man. Their names have been assigned on the basis of their topo- 

 graphical ralations. 



M. scalenus brevis anterior (fig. 16): From the anterior tubercle of 

 the transverse processes of C 4 to 6 there arise an equal number of 

 tendinous digitations A\hich soon become fleshy. The lower bundle is 

 stronger and the distal margin of the muscle thicker. The transversely 

 compressed belly descends do\\-n and forward in front of the roots of 

 the brachial plexus and the subclavian artery. Insertion is on the 

 pleural border of rib 1, by short tendinous fascicles, at the junction 

 of the anterior A\ith the intermediate third of the costal shaft. 



