508 COMPARATIVE PHYSIOLOaY. 



very varying character^ no doubt, with different groups of ani- 

 mals. In a sense, all mamm&ls may see alike, and, in another 

 sense, they may see things very differently ; for, if we may judge 

 by the differences in this respect between educated and unedu- 

 cated men, the great dissimilarity lies in the interpretation of 

 what is seen ; in a word, the cortex has to do with the perfect- 

 ing of visual impulses. Nevertheless, a break anywhere in the 

 long and complicated chain of processes must lead to some 

 serious impairment of vision. Much of the same sort of reason- 

 ing applies to the other senses and also to speech. 



To speak, therefore, of a visual center or a speech center in 

 any very restricted sense is unjustifiable ; at the same time, it 

 is becoming clearer that there is in the occipital lobe, rather 

 than in other parts of the cortex, an area which takes a pecul- 

 iar and special share in elaborating visual impulses into visual 

 sensations and perceptions ; and there can be little doubt 

 that the other senses are represented similiarly in the cerebral 

 cortex. 



The Cerebellum. — Both physiological and pathological re- 

 search point to the conclusion that the cerebellum has an im- 

 portant share in the co-ordination of muscular movements. 

 Ablation of parts of the organ leads to disordered movements ; 

 and, when the whole is removed in the bird, co-ordination is 

 all but impossible, and the same holds for mammals. Section 

 of the middle peduncle of one side is liable to give rise to roll- 

 ing forced movements. In fact, injury to the cerebellum causes 

 symptoms very similar to those following section of the semi- 

 circular canals, so that many have thought that in the latter 

 case the cerebellum had itself been injured. 



Pathological. — Tumors and other lesions frequently, though 

 not invariably, give rise to unsteadiness of gait, much like that 

 affecting an intoxicated person. It may safely be said that the 

 cerebelliun takes a very prominent share in the work of the 

 muscular co-ordination of the body. 



As has already been pointed out, several tracts of the spinal 

 cord make' connection with the cerebellum, and it is not to be 

 forgotten that this part of the brain has, in general, most ex- 

 tensive connections with other regions. Insufficient study has 

 as yet been given to the cerebellum, and it is likely that the 

 part it takes in the functions of the encephalon is greater than 

 has yet been rendered clear. The old notion that this organ 

 bears any direct relation to the sexual functions seems to be 



