528 THE NERVOUS SYSTEM. 



see, hear, and feel pain, to all appearance, as perfectly as 

 before (Mourens ; Magendie). So that, although the resti- 

 form tracts of the medulla oblongata, which themselves 

 appear so sensitive, enter the cerebellum, it cannot be re- 

 garded as a principal organ of sensibility. 



In reference to motion, the experiments of Longet and 

 most others agree that no irritation of the cerebellum 

 produces movement of any kind. Remarkable results, 

 however, are produced by removing parts of its substance. 

 Mourens (whose experiments have been abundantly con- 

 firmed by those of Bouillaud, Longet, and others) extir- 

 pated the cerebellum in birds by successive layers. Feeble- 

 ness and want of harmony of the movements were the 

 consequence of removing the superficial layers. When he 

 reached the middle layers, the animals became restless 

 without being convulsed ; their movements were violent 

 and irregular, but their sight and hearing were perfect. 

 By the time that the last portion of the organ was cut 

 away, the animals had entirely lost the powers of spring- 

 ing, flying, walking, standing, and preserving their equi- 

 librium. When an animal in this state was laid upon its 

 back, it could not recover its former posture ; but it 

 fluttered its wings, and did not lie in a state of stupor ; it 

 saw the blow that threatened it, and endeavoured to avoid 

 it. Volition, sensation, and memory, therefore, were not 

 lost, but merely the faculty of combining the actions of the 

 muscles ; and the endeavours of the animal to maintain its 

 balance were like those of a drunken man. 



The experiments afforded the same results when repeated 

 on all classes of animals ; and, from them and the others 

 before referred to, Mourens inferred that the cerebellum 

 belongs neither to the sensitive nor the intellectual appa- 

 ratus ; and that it is not the source of voluntary movements, 

 although it belongs to the motor-apparatus; but is the organ 

 for the co-ordination of the voluntary movements, or for 

 the excitement of the combined action of muscles. 



