496 



MAMMALIA. 



except the toothed whales in which there are no olfactory nerves. 

 It is effected by the mucous membrane which covers the^ethmo- 

 turbinal bone of the nasal labyrinth ; it is in this mucous mem- 

 brane that the olfactory nerve fibres terminate. The two nasal 



FIG. 263. Mammalian brains (from Claus). a brain of rabbit, dorsal view ; the roof of 

 the right hemisphere is cut away, so as to expose tho 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 cerebellum has been removed, d brain of orang. Cb cerebellum ; H hypophysis 

 cerebri ; Lo olfactory lobe ; Mh corpora quadrigemina ; Mo medulla oblongata ; Sr 

 sinus rhomboidalis ; Th optic thalamus ; Vh cerebral hemispheres ; V root of trigeminal 

 nerve ; II roots of optic, VII, VIII of facial and auditory nerves. 



cavities, which are separated by the median nasal septum, 

 communicate with the nasal passages passing from the external 

 nostrils to the internal narial openings. They also often com- 

 municate with spaces in 'the adjacent cranial and facial bones 



