814 THE CORPORA QUADRIGEMINA. [BOOK in. 



tions of the skeletal muscles (the visceral muscles do not seem 

 to be affected) ; but observers are not agreed as to what that 

 influence exactly is or exactly how it is brought about. The 

 view has been put forward that influences from the cerebellum 

 reinforce so to speak the voluntary impulses proceeding to the 

 muscles, regulate the fusion of the several constituent simple 

 contractions into the sustained muscular effort, which as we 

 have seen is of the nature of a tetanus, and further, so affect the 

 nutrition of the muscle, as to keep up that proper tone of the 

 muscle ( 470) which is a necessary condition of successful 

 muscular action. But according to some observers an animal 

 which from removal of the cerebellum has become highly irreg- 

 ular in its general movements, can carry out a particular muscu- 

 lar act with complete success, can for instance grasp powerfully 

 and firmly with the hand : in such an act the voluntary impulses 

 must reach the muscle in full force, the muscular sense belong- 

 ing to the muscles used must be in full play, and it may even 

 be argued that no marked loss of tone in the particular muscles 

 can be present. If this be so, obviously the unsteadiness of the 

 movements in general must have some other explanation than 

 the one given above. 



Though some have maintained that injury to the cerebellum 

 must be unsym metrical, must be on one side only or more on 

 one side than the other, in order to produce its effects, this does 

 not seem to be the case. Again while some have maintained 

 that injury to the median region is especially effective, others 

 deny this. Indeed so far as we can judge at present, there is 

 no localization of function in the various regions of the cere- 

 bellar cortex ; all the cortex may be said, as used to be said of 

 the cerebral cortex, to 'act as a whole.' Lastly, in respect to 

 the relations of the cerebellum to the cerebrum, it should be 

 noted that removal of one half of the cerebellum has appeared 

 to produce an effect on the crossed cerebral hemisphere, of such 

 a kind that that hemisphere is more readily excitable towards 

 electric and other stimuli, the effect lasting long after the opera- 

 tion of removal. In this connection it is worthy of notice, that 

 congenital deficiency, or atrophy of the cerebral hemisphere of 

 one side, is frequently accompanied by a corresponding defi- 

 ciency of the crossed cerebellar hemisphere. 



513. Both the anterior and posterior corpora quadrigemina 

 are complex in structure ; not only do they differ from each 

 other, but also in each the grey matter differs in different parts, 

 both as to its nature and appearance and as to its connections 

 with tracts of fibres. If we have little right to speak of the 

 ' functions of the cerebellum,' we have even less right to speak 

 of the ' functions of the corpora quadrigemina ' or of either pair 

 of them. The anterior pair, as we have seen, has to do in some 

 way with vision ; but we have reason to think that a part only of 



