NERVOUS SYSTCM OV VERTEBRATA. 499 



given of this organ in various species, selected as 

 specimens from each class, viewed from above ; 

 and in all of which I have indicated corresponding 

 parts by the same letters of reference. 



The portion (m) of the brain, which appears as 

 the immediate continuation of the spinal cord (s), 

 is termed the medulla oblongata. The single tuber- 

 cle (c), arising from the expansion of the posterior 

 columns of the spinal cord, is termed the cere- 

 bellmn, or little brain. Next follow the pair (t), 

 which are termed the optic tubercles, or lobes* and 

 appear to be productions from the middle columns 

 of the spinal cord. These are succeeded by ano- 

 ther pair of tubercles (h), which are called the 

 cerebral hemispheres, 2iud the origin of which maybe 

 traced to the anterior columns of the spinal cord. 

 There is also generally found, in front of the 

 hemispheres, another pair of tubercles (o), which, 

 being connected with the nerves of smelling, have 

 been called the olfactory lobes, or tubercles. Several 

 cavities, termed Ventricles, are found in the interior 

 of the principal tubercles of the brain ; they appear 

 to be formed by the apposition of the surfaces of 

 the masses composing the brain, which are folded 

 upon one another, leaving spaces lined by the pia 

 mater, the surfaces being moistened by a fluid 

 secretion. These are the principal parts of the 

 cerebral mass to be here noticed ; for 1 purposely 

 omit the mention of the minuter divisions, which, 

 though they have been objects of much attention to 

 anatomists, unfortunately furnish no assistance in 



* In the Mammalia, and iu Man, they have been often designated 

 by the very inappropriate name of Corpora quadriyemina. 



