86 DEVELOPMENT OF THE CEREBRUM. INTELLIGENCE. 



that the largest of its masses, the brain proper, consisting 

 of the cerebral hemispheres, and the cerebellum, acquires 

 such a size and relative importance, as to throw the others into 

 the shade. It is therefore necessary to select for comparison, 

 the nervous system of the lowest Fishes ; and here we find a 

 very remarkable correspondence. For the cerebral hemispheres 

 (ch, Fig. 41), and cerebellum (c0), are here in a comparatively 

 undeveloped state ; and of the nervous masses contained in the 

 head, the optic and olfactive ganglia (ol and op) which are 

 analogous to the cephalic ganglia of Insects and Mollusca (Figs. 

 34 and 36), are seen to form at least as considerable a part. 

 The spinal cord of Yertebrata is evidently analogous to the chain 

 of ganglia in the bodies of the Articulata ; so that between 

 the lowest type of the nervous system in the former, and its 

 regular plan in the latter, there is little essential difference. 

 But as we ascend the Vertebrate series, towards Man, we find 

 the cerebrum becoming larger and larger ; until it acquires a 

 size and importance, which for a long time induced the belief 

 among Physiologists, that it is the essential portion of the 

 nervous system, the only centre of nervous power. This has 

 been fully proved, however, not to be the case ( ANIM. PHYSIOL., 

 Chap. X.) ; a very large class of actions, including all those 

 immediately concerned in the maintenance of life, being still 

 performed when the cerebral hemispheres had been removed. 



64. Upon comparing the relative development of this organ, 

 in different Vertebrated animals, with the mental faculties whose 

 possession they respectively manifest, it is difficult to avoid the 

 conclusion, that the Cerebrum is the instrument of Intelligence ; 

 whilst the other portions of the nervous centres minister to 

 Instinctive actions. It has been pointed out (ANIM. PHYSIOL. 

 72) that the high development of the instincts is the prominent 

 character of the Articulata ; and that what we regard as the 

 highest perfection of their structure, tends in this direction. On 

 the other hand, there is a tendency among the Yertebrata to 

 the removal of the animal from the dominion of undiscerning 

 uncontrollable instinct, and to place all its operations under the 

 dominion of an intelligent Will. We no longer witness in these 



