KEPTILIA. 



577 



smooth and without convolutions; and they are hollowed out into 

 capacious ventricular chambers, in which are contained the corpus 

 striatum and choroid plexus (j#g. 262, c), and the two sides are 

 moreover brought into communication by an anterior and posterior 

 commissure. 



The optic lobes (e) are as yet uncovered by the extension of 

 the hemisphere backwards ; and each, when laid open, is found to 

 enclose a ventricle {Jig. 262, c). The cerebellum (a) is still 

 small, and consists but of the median portion : behind it is a sup- 

 plementary lobe (g), extending over the fourth ventricle, as in 

 Fishes. The student will easily recognise the pituitary body (f) ; 

 but neither this, nor the origins of the nerves, present any pecu- 

 liarity worthy of more particular description. 



Fig. 262. 



Taking the cerebral nerves in the order in which they arise, we 

 will now proceed briefly to trace their general distribution ; and 

 this we shall find to correspond most exactly in all essential points 

 throughout the different classes of Vertebrata. 



The olfactory nerves leave the olfactory lobes of the brain as 

 single round cords ; and are not, as in the Mammalia, divided into 



2 p 



