CHAP. XVII.] THE BRAIN OF QUADRUMANA. 301 



Orang, and it was also absent in the young Hamburg 

 Gorilla. 



The three principal Fissures already referred to, viz., 

 the Sylvian, that of Rolando, and the External Perpen- 

 dicular, divide the outer surface of the Hemisphere into 

 four Lobes, in the manner already described (p. 292) ; 

 and though their relative size is very different in the several 

 creatures in which they exist, these Lobes may be considered 



3. cm 



Fin. 120. Brain of Gorilla, longitudinal section, inner aspect. (BolauandPansch.) 

 s. cm, Calloso-marginal Fissure ; /. p, Internal Perpendicular Fissure ; /. c, Calcarine 

 Fissure, being the posterior part of the ' Fissure of the Hippocampus.' 



to represent strictly homologous parts in inferior Monkevs, 

 in higher Apes, and also in the Brain of Man. 



Concealed by the lips of the Sylvian fissure, and form- 

 ing part of its floor, we may find the small Central Lobe, 

 commonly known as the * Island of Reil.' This part be- 

 comes well marked and even complex in Man, and, accord- 

 ing to Flower,* is traceable, except in the diminutive 

 Marmoset, throughout the Quadrumanous series, though 

 it is absent in all other Mammalia. 



* " Trans, of Zoolog. Soc., 1866," vol. v. p. 108. 



