404 



PHYSIOLOGICAL SERIES. 



D. 585. The brain of a Cebus (sp.). 



The left cerebral hemisphere has been separated ond the 

 dorsal operculum of the Sylvian fissure removed to show 

 the extent of the insula. The mesial lip of the intraparietal 

 sulcus (in the region of its bend) has been removed to 

 show that the parieto-occipital sulcus does not become 

 confluent with the ramus parieto-occipital is sulci intra- 

 parietalis, but merely cuts into its posterior wall. 



On the right hemisphere the inferior lip of the Sylvian 

 fissure has been cut away to show how the superior limiting 

 sulcus of Reil ends anteriorly. 



This is a small and correspondingly simple brain for a 

 Cebus. The sulci rectus and arcuatus have fused to form a 

 simple bow. The Simian sulcus is especially diminutive 

 and is quite independent of the ramus transversus occipitalis 

 of the intraparietal sulcus. 0. C. 1337 K. 



D. 586. The brain of a Humboldt's Woolly Monkey (Lagotlmx 

 liumboldti), (<?), (figs. 239, 240). 



SULC. ARC. 



Fig. 239. (x|.) 



SULC. CENT. 



SULC. RECT 



SULC. INTRAPAR. 



SULC. ORB 



SULC. INF. TEMP. 



SULC. PAR. 



This brain still further demonstrates the extreme in- 

 stability of the region of the parieto-occipital sulcus. The 

 tension of the expanding cortex in this region of the 

 Primalr hemisphere may be relieved by the development 

 of a deep sulcus which may be derived from the intra- 

 parietal system (as in Cebus, where we have seen tin- ramus 

 parieto-occipitalis), or from the Simian sulcus (as in many 

 Cercopithecida?), or, as in this case, by a great extension 

 and deepening of the parieto-occipital sulcus. The latter 



