Chap. XVI.] 



SOME OTHER MAMMALS. 



2G7 



wise well developed hollow structures, as they are in many 

 Keptiles. The size of the ' pyriform processes ' in Quad- 

 rupeds is, in fact, generally in direct relation with that 

 of the Olfactory Lobes, and these are especially well 

 developed in Eodents, Euminants, and certain Carnivores, 

 while they are ab- 

 sent altogether in 

 some of the Ce- 

 tacea (fig. 74). 



The more mi- 

 nute description c 

 of the external 

 surface of the 



Cerebral Hemi- Fig.S2. -Head and brain of caSquirrel, side view. (Solly.) 

 , . A, Olfactoiylobe; b, Cercbr il hemisphere ; e. Cerebellum ; 



spheres, compris- h, spinai cord. 

 ing some account 



of their * fissures,' 'lobes,' and 'convolutions,' may for 

 the moment be deferred, till we have first given some 

 attention to the Ventricles, Commissures, and other inter- 

 nal parts of the Brain. 



Internal Topography of the Brain in Quadrupeds 

 and some other Mammals. 



Each Cerebral Lobe or Hemisphere contains a Lateral 

 Ventricle, the size and shape of which is very variable — 

 these being in great part dependent upon the general 

 form of the Hemispheres, and upon the relative size and 

 shape of the ganglionic prominences which the Ventricles 

 contain. As already mentioned, in Quadrupeds possessing 

 very large Olfactory Lobes, prolongations of the Lateral 

 Ventricles extend into them through their ' peduncles,' 

 from those spurs which stretch downwards into the corre- 

 spondingly developed ' pyriform processes.' 



