RELATIVE DEVELOPMENT OF THE CEREBRUM. 517 



the Cerebral Hemispheres are far from being the essential parts of the 

 apparatus they were formerly imagined to be ; and that they are, on 

 the contrary, superadded organs, of which we find no distinct represen- 

 tatives in the Invertebrata, and of which the first appearance (in the 

 class of Fishes) exhibits them in the light of appendages, destined to 

 perform some special function peculiar to Vertebrated animals. The 

 results of the removal of the Cerebral Hemispheres, in animals to which 

 the shock of the operation does not prove immediately fatal, fully con- 

 firms this view ; and must appear extraordinary to those, who have 

 been accustomed to regard these organs as the centre of all energy. 

 Not only Reptiles, but Birds and Mammalia, if their physical wants be 

 supplied, may survive the removal of the whole Cerebrum for weeks, or 

 even months. If the entire mass be taken away at once, the operation 

 is usually fatal ; but if it be removed by successive slices, the shock is 

 less severe, and the depression it produces in the organic functions is 

 soon recovered from. It is difficult to substantiate the existence of 

 actual sensation in animals thus circumstanced ; but their movements 

 appear to be of a higher kind, as already remarked ( 903), than those 

 resulting from mere reflex action. Thus they will, eat food, when it is 

 put into their mouths ; although they do not go to seek it. If violently 

 aroused, the animal has all the manner of one waking from sleep ; and 

 it manifests about the same degree of consciousness as a sleeping 

 Man, whose torpor is not too profound to prevent his suffering from an 

 uneasy position, and who '-moves himself to amend it. In both cases, 

 the movements are consensual only, and do not indicate any voluntary 

 power ; and we may well believe that, in the former case as in the 

 latter, though felt they are not remembered; an active state of the 

 Cerebrum being essential to memory, though not to sensations, which 

 simply excite certain actions. When the Cerebral Hemispheres are 

 being removed, slice by slice, it is noticed that injuries of these organs 

 neither occasion any signs of pain, nor give rise to convulsive move- 

 ments. Even the Thalami and Corpora Striata may be wounded, 

 without the . excitement of convulsions ; whilst, if the incisions involve 

 the Tuberqula Quadrigemina, convulsions uniformly occur. It has been 

 often observed in Man, that, when it has been necessary to separate 

 protruded portions of the brain from the healthy part, no sensation was 

 produced, even though the mind was perfectly clear at the time. Hence 

 it would appear that neither is the Cerebrum itself the centre of sensa- 

 tion, nor is it so connected with that centre, as to be able to convey to 

 it sensory impressions of an ordinary kind. This is analogous to the 

 condition of the nerves of special sense, as already remarked. That no 

 irritation of the cerebral substance should excite convulsive movements, 

 is a very remarkable circumstance ; and it seems to indicate, that the 

 changes which mental operations produce in the cerebral fibres, cannot 

 be imitated, as changes in other motor fibres may be, by physical im- 

 pressions. 



913. As already stated, the relative amount of Intelligence in diffe- 

 rent animals bears so close a correspondence with the relative size and 

 development of the Cerebral Hemispheres, that it can scarcely be ques- 

 tioned that these constitute the organ of the Reasoning faculties, and 



