CHAPTER XVII. 



THE BRAIN OF QUADBUMANA. 



THE Brains of Lemurs, Monkeys, Baboons and Apes, 

 present many common characters, which testify to the 

 close relationship of these several forms with one another. 

 A sort of gradation, though not that of a single series, is to 

 be met with. Beginning in the Lemurs, with a brain 

 whose structure is only little removed from that of 

 Rodents, we may pass by means of most distinct transi- 

 tion forms to the more highly evolved Cerebral Hemi- 

 spheres of the great ' man-like ' Apes the Chimpanzee, 

 the Gorilla, and the Orang-utan. 



A certain community of structure is perceptible 

 throughout the whole series. The brain of every Quad- 

 rumanous animal is distinguished from that of Quad- 

 rupeds by certain well-defined characters. Structures 

 previously existing no longer manifest themselves ; while, 

 on the other hand, new parts become differentiated from 

 the old, so as to present themselves as more or less in- 

 dependent structures. 



The structures existing in many Quadrupeds, but not 

 met with in Quadrumana, are these : 



1. Prolongations from Lateral Ventricles into Olfactory Lobes. 



2. Distinct ' pyriform processes ' (< r ' hippocampal lobes ') on the 



under surface of the Temporal Lobes. 



3. The so-called ' trapezoid bodies ' of the Medulla Oblongata.* 



* Some traces of these structures still exist in the Howler Monkey. 



