o - 



Chap. XVII] THE BRAIN OF QUADRUMANA. 287 



The additional characters or newly-differentiated parts 

 met with among Quadrumana, but absent in lower brutes, 

 may be thus enumerated : — 



(1.) The differentiation of a distinct Posterior (or 

 ' Occipital ') Lobe in each of the Cerebral Hemispheres, 

 contaiuing in its interior a ' posterior horn ' or ' cornu ' of 

 the Lateral Ventricle, which is marked by a more or less 

 distinct projection (' Hip- 

 pocampus Minor ') corre- 

 sponding with a fissure on 

 the inner surface of this 

 lobe.* The development of 

 this Posterior Lobe causes ^_ 

 the Cerebral Hemispheres c ^-\f' ^^ 

 to extend so far backwards t "^ 



as to cover the greater part ^'«- 102.-The Brain of the Brown Macaque 

 ^ ^ (Macacus nemestrinus), side view. F, Frontal 



or the whole of the Cere- L)be; P, Parletal Lobe ; O, Occipital Lobe; 

 111 C, Cerebellum. /, /, Greatly prolonged Fis- 



DeiiUm. sy^g yf Sylvius. 



(2.) The appearance of 

 certain ' primary ' Cerebral Fissures, similarly disposed in 

 all Quadrumana, and the gradual development of other 

 * secondary ' and ' tertiary ' Fissures — the whole series of 

 depressions serving to divide the surfaces of the Hemi- 

 spheres into Lobes and Convolutions according to a new 

 but constant and definite pattern. This differs notably from 

 the two principal convolutional patterns of Quadrupeds, 

 though it agrees in all essential respects with what we 

 shall find — though in a more developed form — in the 

 Human Brain. 



(3.) The existence of a Central Lobe, corresponding 

 with the part known in Man as the ' Island of Pteil.' 



(4.) Another additional character is of less importance, 



* The Seal is the only Quadruped in which a ' posterior cornu' 

 is known to exist, as a prolongation irom each Lateral Ycnlricle. 



