CHAP. IL] THE BRAIN. 1005 



of its cerebral hemisphere mainly to shew that in this warm- 

 blooded animal, as in the more lowly cold-blooded frog, the parts 

 of the brain below or behind the cerebral hemispheres constitute 

 a nervous machinery by which all the ordinary bodily movements 

 may be carried out. The bird, like the frog, suffers no paralysis 

 when the cerebral hemispheres are removed; on the contrary, 

 though its movements have not been studied so closely as those of 

 the frog, the bird without its cerebral hemispheres seems capable 

 of executing at all events all the ordinary bodily movements of a 

 bird. And in the bird as in the frog, the afferent impulses 

 passing into the central nervous system, whether they give rise to 

 consciousness or no, play an important part not only in originating 

 but in guiding and coordinating the efferent impulses which stir 

 the muscles to contract, the coordination being effected partly in 

 the spinal cord, but largely and indeed chiefly in the parts of the 

 brain lying behind the cerebral hemispheres. It is further worthy 

 of notice that spontaneity of movement of the kind which we have 

 described, is much more prominent in the more highly developed 

 bird, than in the more lowly frog. The cerebral hemispheres are 

 not the only part of the central nervous system which has under- 

 gone a greater development in the bird ; the other parts of the 

 brain have also acquired a far greater complexity than in the frog. 

 640. In the mammal the removal of the cerebral hemi- 

 spheres is still more difficult than in the bird ; the animal cannot 

 be kept alive for more than a few hours ; but in some mammals it 

 is possible to observe during those few hours phenomena kindred 

 to those witnessed in the bird and in the frog. The rabbit or rat, 

 from which the whole of both hemispheres has been removed 

 with the exception of the parts immediately surrounding the optic 

 thalami, can stand, run and leap. Placed on its side or back it at 

 once regains its feet. Left alone it generally remains as motion- 

 less and impassive as a statue, save now and then when a passing 

 impulse seems to stir it to a sudden but brief movement ; but 

 sometimes it seems subject to a more continued impulse to move, 

 in which case death usually follows very speedily. Such a rabbit 

 will remain for minutes together utterly heedless of a carrot or 

 cabbage-leaf placed just before its nose, though if a morsel be 

 placed within its mouth it at once begins to eat. When stirred it 

 will with ease and steadiness run or leap forward ; and obstacles 

 in its course are very frequently, with more or less success, avoided. 

 In some cases the animal (rat) has been described as following by 

 movements of the head a bright light held in front of it (provided 

 that the optic nerves and tracts have not been injured during the 

 operation), as starting when a shrill and loud noise is made near 

 it, and as crying when pinched, often with a long and seemingly 

 plaintive scream. So plaintive is the cry which it thus gives 

 forth as to suggest to the observer the existence of passion, 

 this, however, is probably a wrong interpretation of a vocal action ; 



