496 THE BKAIN. 



agitated with ineffectual movements, which are evidently voluntary in 

 character, but are at the same time irregular and confused. 



The direct inference which may be derived from these phenomena is 

 that the power of co-ordination or association of voluntary movements 

 of the body and limbs resides in the cerebellum as a nervous centre, and 

 that this power is accordingly lost or impaired by injury of its sub- 

 stance. It is evident that such a power really exists under some form 

 in the nervous system. No natural co-ordinated movements are effected 

 by the independent contraction of separate muscles, but always by a 

 number of muscles, or groups of muscles, acting in harmony with each 

 other. The extent and variety of this muscular association vary in 

 different classes of animals. They are very considerable in birds and 

 quadrupeds as compared with fish and reptiles, and reach in man their 

 highest grade of development. Even in maintaining the ordinary pos- 

 tures of standing or sitting, many different muscles are brought into 

 action together, in each of which the degree of contraction must be 

 accurately proportioned to that of the others. In the motions of walk- 

 ing and running, or in the still more delicate movements of the hands 

 and fingers, this harmony of action is indispensable to the efficiency of 

 the muscular apparatus. 



Notwithstanding the fact that this power of co-ordination is invariably 

 disturbed by injuries of the cerebellum, it is doubted by some writers 

 whether it can be strictly attributed, as a physiological function, to this 

 particular part of the nervous system. The grounds upon which this 

 doubt is based are twofold ; first the subsequent recovery of the power 

 of co-ordination by animals after injury or partial removal of the cere- 

 bellum, and secondly, the results of certain pathological observations 

 in the human subject. 



I. Eestoration of the Co-ordinating Power in Operated Animals. 

 It is certain that animals may be affected, after partial extirpation of 

 the cerebellum, with well marked loss of co-ordinating power, and that 

 they may, in some instances, subsequently recover this power without 

 regeneration of the lost nervous substance. This recovery was observed 

 by Flourens in the fowl and in the pigeon, and has been seen by Flint 1 

 in the pigeon after removal of about two-thirds of the whole mass of the 

 cerebellum. We have also met with four instances of the same kind. 

 In the first, about two-thirds of the cerebellum was taken away by an 

 opening in the posterior part of the cranium. Immediately afterward, 

 the pigeon showed all the usual effects of the operation, being incapable 

 . of flying, walking, or even of standing still, but only reeled and sprawled 

 in a perfectly helpless manner. In five or six days from that time, he 

 had regained a very considerable control over the voluntary movements, 

 and at the end of sixteen days his power of muscular co-ordination was 

 so nearly perfect, that its deficiency, if any existed, was imperceptible. 

 He was then killed ; and on examination, it was found that his cerebel- 



1 The Physiology of Man ; Nervous System. New York, 1872, p. 367. 



