556 THE SENSORIAL FUNCTIOxNS. 



ductions from the middle columns of the spinal 

 marrow. These are succeeded by another pair 

 of tubercles (h), which are called the cerebral 

 hemispheres, and the origin of which may be 

 traced to the anterior columns of the spinal 

 marrow. There is also generally found, in front 

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

 which, being connected with the nerves of smell- 

 ing, have been called the olfactory lobes, or 

 tubercles* These are the principal parts of the 

 cerebral mass to be here noticed ; for I pur- 

 posely omit the mention of the minuter divisions, 

 which, though they have been objects of much 

 attention to anatomists, unfortunately furnish no 

 assistance in understanding the physiology of 

 this complicated and wonderful organ. 



On comparing the relative proportions of the 

 brain and of the spinal marrow in the four 

 classes of verteb rated animals, a progressive in- 

 crease in the size of the former will be observed 

 as we ascend from Fishes to Reptiles, Birds, 

 and Mammalia. This increase in the magnitude 

 of the brain arises chiefly from the enlargement 

 of the cerebral hemispheres (h), which in the 

 inferior orders of fishes, as in the Trigla lyra, or 

 Piper Gurnard (Fig. 451), and in the Murccna 

 conger, or Conger Eel (Fig. 452), are scarcely 



* Several cavities, termed Ventricles, are occasionally found 

 in the interior of the principal tubercles of the brain ; but their 

 use is unknown. 



