Chap, ii.] THE BRAIN. 725 



tion, will bury itself in the earth at the approach of Avinter, 

 and is able to catch and swallow flies and other food coming 

 in its neighbourhood, although in other respects it shews no 

 signs of an intelligent volition, and answers with unerring 

 mechanical certainty to the play of stimuli. We may add that 

 in some fishes the removal of their cerebral hemispheres, which 

 in these animals form a relatively small part of the whole brain, 

 produces exceedingly little change in their general behaviour. 



These however are not the considerations on which we wish 

 here to dwell ; we have quoted the behaviour of the bird 

 deprived 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, suf- 

 fers 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 lias undergone a greater development in the bird ; the 

 other parts of the brain have also acquired a far greater com- 

 plexity than in the frog. 



§ 476. In the mammal the removal of the cerebral hemi- 

 speres 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 sur- 

 rounding 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 motionless 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 



