CHAP. XVII.] THE BRAIN OF QUAD RUM AN A. 5J87 



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, 

 containing in its interior a ' posterior horn ' or l 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 

 to extend so far backwards 

 as to cover the greater part FlG - 102 -- The Brain of the Brown Macaque 



5 r (Macacus nemestrinus). side view. F, Frontal 



Or the Whole Of the Cere- Lobe; P, Parietal Lobe; O, Occipital Lobe; 



"Kollnm C> Ceretellum - / /> Greatly prolonged Fis- 



Im ' sure of 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 Reil.' 



(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 from each Lateral Ventricle. 



