174 



COMPARATIVE ANATOMY 



Marsupials),! ^g usually a large and important structure; its 

 relative size is in inverse proportion to that of the anterior 

 commissure. lu addition to the anterior and posterior commis- 

 sures, a middle commissure is definitely differentiated from the 



Ul| IV |V |VU1| X XI ; 



p.v. vi vii ix xii 



Fig. 143.— Brain of Rabbit. (A, dorsal ; B, ventral ; and C, lateral view.) 



/. h. , cerebral hemispheres ; m.h., optic lobes ; h.l}., cerebellum ; c.h'., superior 

 vermis, and c. h". , lateral lobe of cerebellum ; nid. , medulla oblongata ; ep. , 

 pineal body ; h.p., hypophysis ; jou. , pons Varolii ; cr., crura cerebri ; /,p. , 

 pallial fissure ; b.o., olfactory bulb ; i-xii, cerebral nerves. 



base of the brain as a distinct structure connecting the two optic 



thalami. 



In correspondence with the division of the hemispheres into 



lobes, there is a marked differentiation of the lateral ventricles, 



' Recent researches indicate that a true corpus callosum is present only in 

 the Placentalia, and that the commissure which is usually supposed to represent 

 it in lower types may be more correctly described as the hipiMcampal commissure. 



