XI FUNCTIONS OF CEREBRAL HEMISPHERES 525 



can rest ; and when placed on its back immediately turns 

 over and resumes its natural position. Not only so, but 

 the following very striking experiment may be performed 

 with it. Placed on a small board it remains perfectly 

 motionless so long as the board is horizontal ; if, however, 

 the board be gradually tilted up so as to raise the animal's 

 head, directly the board becomes inclined at such an 

 angle as to throw the frog's centre of gravity too much 

 backwards, the creature begins slowly to creep up the 

 board, and, if the board continues to be inclined, wUl at 

 last reach the edge, upon which when the board becomes 

 vertical he will seat liimself with apparent great content. 

 Nevertheless, though his movements when they do occur, 

 are extremely weU combined and apparently identical 

 with those of a frog possessing the whole of his brain, 

 he never moves spontaneously, and never stirs unless 

 irritated. 



Thus the parts of the brain below the cerebral hemi- 

 spheres constitute a complex nervous machinery for 

 carrying out intricate and orderly movements, in which 

 aflerent impulses play an important part, though they 

 do not give rise to clear or permanent affections of 

 consciousness. 



There can be no doubt that the cerebral hemispheres 

 are the seat of powers, essential to the production of 

 those phenomena which we term intelligence and will ; 

 and there is experimental and other evidence which seems 

 to indicate a connection between particular parts of the 

 surface' of the cerebral hemispheres, and particular acts. 

 Thus irritation of particular spots in the anterior part of 

 a dog's brain will give rise to particular movements of 

 this or that limb, or of this or that group of muscles ; and 

 the destruction of a certain part of the posterior lobes of 

 the cerebral hemispheres is said to cause blindness. But 

 the exact way in Avhich these effects are brought about is 

 not yet thoroughly understood ; and even if it should be 

 ultimately proved beyond all doubt, that the central end- 



