282 



MAMMALIA. 



The nervous system (fig. 671) is characterised by the size and high 

 development of the brain, the hemispheres of which are so large that 

 they not only fill the anterior part of the cranial cavity, but even 



I 



Lo 



FIG. 671. Brains of Mammalia, a, Brain of rabbit, from above ; the roof of the right hemi- 

 sphere is removed so as to expose the lateral ventricle, b, The same from below, c, 

 Brain of cat ; on the right side the lateral and posterior part of the hemisphere is 

 removed, and almost as much on the left side, and the greater part of the hemispheres 

 of the cerebellum have been removed, d, Brain of orang (a, b, c, after Gegenbaur ; d, 

 from the regne animal). Vh, cerebral hemispheres ; Mh, corpus quadrigeminum ; Cb, 

 cerebellum; Mo, medulla oblongata; Lo, olfactory lobe; II, optic nerve; V N, tri- 

 geminal; VII VIII, facial and auditory nerves; H, hypophysis cerebri; Th, optic 

 thalamus ; Sr, sinus rhomboidalis. 



partly cover the cerebellum. In the Marsupials and Monotremes 

 the surface of the hemispheres is still smooth ; but in the Edentates, 

 Rodents, and Insectivores it is marked by depressions and ridges, 

 which in the higher forms become regular furrows (sulci) and convo- 



