JUNCTIONS OF THE fcxcEPHALosf. 209 



clitlon. This state of immobility, however, is not accompanied 

 by the loss of sight, of hearing, or of ordinary sensibility. 

 All these functions remain, as "well as that of voluntary 

 motion. If a pistol be discharged behind the back of the 

 animal, he at once opens his eyes, moves his head half round, 

 and gives evident signs of having heard the report; but he 

 immediately becomes quiet again, and pays no further atten- 

 tion to it. ... Longet has found that by moving a 

 lighted candle before the animal's eyes in a dark place, the 

 head of the bird will often follow the movements of the 



candle from side to side, or in a circle The 



limbs and muscles are still under the control of the will ; but 

 the will itself is inactive, because, apparently, it lacks its 

 usual mental stimulus and direction." 



It is difficult, however, to say how far that part of the 

 nervous system extends on which the existence of conscious- 

 ness is dependent. Possibly it reaches over a greater area 

 in the lower than the higher animals. A decapitated frog 

 can be made to leap, and will thrust objects aside when 

 irritated; and although these movements are sometimes said 

 to be reflex, it is not easy to understand how they can be 

 so. But, undoubtedly, all the higher manifestations of con- 

 sciousness which constitute intelligence, depend on the 

 cerebral hemispheres. On comparing different kinds of 

 mammals, it is found that increased development of the 

 hemisperes and complexity of the convolutions into which 

 their surface is thrown are associated with increased intelli- 

 gence. In rodent animals, such as rabbits, the hemispheres 

 are small and smooth, while in apes, they are proportionally 

 larger, and are more highly convoluted than in any animal 

 but man. Even in the higher races of men, the convolutions 

 are more complex than in the lowest. The circumstance 

 that disease of the grey matter of the hemispheres is liable 

 to be accompanied with intellectual derangement, likewise 

 points to a connection between the hemispheres and intelli- 

 gence. 



But if the sensorium, or seat of consciousness, be confined 



to the encephalon, the question arises : How do we become 



aware of impressions made at the surface of the body? The 



old physiologists believed in the diffusion of consciousness 



H o 



