682 FUNCTIONS OF THE CEREBELLUM. [CH. XLIX. 



of the working of the muscles which maintain the body in a 

 position of equilibrium. 



It must not be supposed from this that the cerebellum is the 

 sole centre for co-ordination. We have already seen that all the 

 machinery necessary for carrying out very complicated locomotive 

 movements is present in the spinal cord. The higher centres set 

 this machinery going, and the work of arranging what muscles 

 are to act, and in what order, is carried out by the whole of the 

 grey matter from the corpora striata to the end of the spinal 

 cord, including such outgrowths as the corpora quadrigomina and 

 cerebellum. An instance of a complex co-ordinated movement is 

 seen in what we learnt to call in the last chapter conjugate 

 deviation of head and eyes. The higher "cortical centre gives the 

 general word of command to turn the head and eyes to the right : 

 the subsidiary centres or subordinate officials arrange that this 

 is to be accomplished by the external rectus of the right eye 

 supplied by the right sixth nerve, the internal rectus of the left 

 eye supplied by the left third nerve, and numerous muscles of 

 neck and back of both sides supplied by numerous nerves. We 

 thus see how the complicated intercrossing of fibres and connec- 

 tions of the centres of the various nerves are brought into play. 



The functions of the cerebellum are investigated by the same 

 two methods of experiment (stimulation and extirpation) that are 

 employed in similar researches on the cerebrum. The anatomical 

 connections of the cerebellum with other parts of the cerebro- 

 spinal axis have been chiefly elucidated by the degeneration 

 method. Each side of the cerebellum has three peduncles ; the 

 superior peduncle connecting it to the opposite hemisphere of the 

 cerebrum, the inferior peduncle connecting it to the same side of 

 the spinal cord, and the middle peduncle contains fibres which 

 link the two halves of the cerebellum together in a physiological 

 though not in an anatomical sense. The inferior peduncle termi- 

 nates in the vermis ; in some of the lower animals the vermis 

 is practically the only part of the cerebellum which is present, 

 and it is this part of the cerebellum which is principally con- 

 cerned in the co-ordination of the bodily movements. The cere- 

 bellar hemispheres are especially connected with the opposite 

 cerebral hemispheres ; and possibly just as the different regions 

 of the body have corresponding areas in the cerebrum, so also 

 they are similarly represented in the cerebellum ; but localisation 

 of function in the cerebellum has not gone sufficiently far yet to 

 make this a certainty. 



After hemi- extirpation, degeneration occurs in the peduncles of the same 

 side ; there are, therefore, no commissural fibres that actually pass from 



