'264 



THE BRAIN OF QUADRUPEDS AND 



cluster of many irregular and deepl}^ foliated lobules." 

 This kind of conformation is represented in fig. 75. In 

 the marvellously active Bat, the Cerebellum is very large 

 in proportion to the size of the Cerebral Lobes — though 

 in this animal it seems to be tiie median portion which 

 becomes so highly developed (fig. 78). 



Between the under surface of the median lobe of the 



Cerebellum 

 and the back 

 of the Medul- 

 la, there is a 

 small lozenge- 

 shaped space, 

 known as the 

 * fourth ven- 

 tricle,' formed 

 by the diver- 

 gence of what 

 were the pos- 

 terior columns 

 of the Spinal 

 Cord, and the 

 consequent 

 opening up 

 of its central 

 canal. The 

 lower extremity of this space may be seen in figs. 79, 80. 

 The size of the Optic Lobes, in proportion to the rest 

 of the Brain, is very much less in Quadrupeds than it is 

 in Birds, and this ratio goes on diminishing as we pass 

 from lower to higher representatives of the former class. 

 These bodies have a greater proportional size in Marsupials 

 and Eodents, for instance, than in Kuminants and Carni- 

 vores. The cavities to be fo^ind in their interior in Birds 



Fin. 77.— Brain of the PorpoLsc, with tlie upper half of the 

 left Hemisphere cut away so as to show the contents of the 

 Lateral Ventricle. (Solly.) 1, Outer wall of Ventricle ; 2, Corpus 

 Btriatum ; 3, Fornix ; 4, 5, anterior and j^osterior segments 

 of quadrigerninal bodies ; 0, corpus callosuni ; 7, Cerebellum ; 

 8, Spinal Cord ; 0, Pineal body. 



