THE CEREBKO-SP1NAL NERVOUS SYSTEM. 527 



touched, pain is indicated; and, if the restiform tracts of the medulla 

 oblongata be irritated, the most acute suffering appears to be produced. 

 It cannot, therefore, be regarded as a principal organ of sensation. 



(2.) Co-ordination of Movements. In reference to motion, the ex- 

 periments of Longet and many others agree that no irritation of the 

 cerebellum produces movement of any kind. Remarkable results, how- 

 ever, are produced by removing parts of its substance. Flourens (whose 

 experiments have been confirmed by those of Bouillaud, Longet, and 

 others) extirpated the cerebellum in birds by successive layers. Feeble- 

 ness and want of harmony of muscular 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 springing, flying, walking, standing, and pre- 

 serving their equilibrium. 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 endeavored to avoid it. Volition and sensation, therefore, were not 

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

 and the endeavors 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, 

 Flourens inferred that the cerebellum belongs neither to the sensory nor 

 the intellectual apparatus; and that it is not the source of voluntary 

 movements, although it be longs to the mot or apparatus; but is the organ 

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

 of the combined action of muscles. 



Such evidence as can be obtained from cases of disease of this organ 

 confirms the view taken by Flourens; and, on the whole, it gains sup- 

 port from comparative anatomy; animals whose natural movements re- 

 quire most frequent and exact combinations of muscular actions being 

 those whose cerebellaare most developed in proportion to the spinal cord. 



We must remember, too, that the cerebellum is connected with the 

 posterior columns of the cord as well as with the direct cerebellar tract, 

 both of which probably convey to the middle lobe muscular sensations. 

 It is also connected with the auditory nerves. Movements of the eyes 

 also occur on direct stimulation of the middle lobe. It seems, therefore, 

 to be connected in some way with all of the chief sensory impulses which 

 have to do with the maintenance of the equilibrium. 



Foville supposed that the cerebellum is the organ of muscular sense, 

 i. e., the organ by which the mind acquires that knowledge of the actual 

 state and position of the muscles which is essential to the exercise of the 



