NERVOUS SYSTEM. VERTEBBATA. 407 



the intraparietal, but on the left side it consists of three 

 fragments, of which only the inferior is united to the main 

 sulcus. 



The ramus occipitalis of the intraparietal is bifid and 

 quite independent of the Simian sulcus. The latter is 

 extensive and irregular on the right side, but is more frag- 

 mentary on the left. It is a simple sulcus, i. e. its posterior 

 lip is not operculated. The lateral occipital sulcus is dis- 

 located to such a ventral position that the inferior occipital 

 sulcus seems to be entirely aborted. 



There is a simple sulcus rectus, not joined to the sulcus 

 arcuatus. The latter gives off a peculiar, extraordinarily 

 long, posterior horizontal branch. Fragmentary repre- 

 sentatives of the superior precentral and superior frontal 

 sulci are present. 



Few Apes possess such a complicated occipital region, 

 with such a complete absence of operculation and, for its 

 size, such a well-furrowed frontal area as Ateles. In these 

 respects the comparison of Ateles and Homo is very 

 instructive. 0. C. 1337 H e. 



Huxley, Proc. Zool. Soc. 1861, p. 247. 



D. 589. The brain of a Black-faced Spider-Monkey (Ateles ater). 



Note again the apparent continuity of Sylvian fissure 

 and intraparietal sulcus, such as occasionally occurs in 

 Lemurs and Apes, with the difference that here there is a 

 submerged gyrus to indicate the line of separation of the 

 overlapping elements. All the superior precentral elements 

 are separate here. 



The Simian sulcus is much larger and deeper here than 

 in the last specimen. This is particularly marked on the 

 right hemisphere, where the posterior lip of the sulcus is 

 obviously operculated. 



The caudal ramus of the arcuate sulcas is much shorter 

 and the central sulcus correspondingly larger than in the 

 last specimen. 



The anterior end of the superior limiting sulcus of Rei) 

 is clearly exposed on the right hemisphere (compare with 

 the Anthropoid Apes). 0. C. 1337 H/. 



