568 



TEXT-BOOK OF PHYSIOLOGY. 



The Results of Experimental Lesions. If the cerebellum in its totality 

 coordinates and harmonizes the action of the muscles on the opposite sides of 

 the body, any derangement of its structure or its connections with the cord, 

 medulla, pons, or basal ganglia should at once be followed by incoordination 

 of muscles and a want of harmony in their action. Experimental lesions of 

 the cerebellum are attended by such results. The phenomena observed are 

 many and complex. They differ in extent and character in different animals 

 and in accordance with the extent and location of the lesion, though the note 

 of incoordination runs through them all. 



FIG. 259. ATTITUDE ASSUMED AFTER DESTRUCTION or THE LEFT HALF OF THE CEREBELLUM. 



(Moral and Doyon, after Thomas.} 



Removal of one lateral half of the cerebellum in the dog is followed by an 

 inability to maintain the equilibrium necessary to the erect position. On 

 attempting to stand, the animal at once falls toward the side of the lesion, the 

 muscles of which at the same time contract and give to the body a distinctly 

 curved condition (Fig. 259). The anterior limbs are extended to the opposite 

 side. On making efforts to regain the standing position, the animal may 



roll over around the long axis of its 

 body. Conjugate deviation of the 

 eyes is frequently observed as well as 

 nystagmus. 



After a few days the symptoms par- 

 tially subside and the animal acquires 

 the power of sitting on the abdomen 

 when the anterior limbs are widely 

 extended (Fig. 260). As the days go 

 by the improvement continues, and the 

 animal recovers the power of walking, 

 though each step is attended with 

 tremor and oscillations of the body. 

 Any change in the center of gravity 

 such as results when one leg is lifted may result in a fall toward the side of 

 the lesion, owing to an inability to promptly bring about the necessary 

 compensatory muscle actions. With time the animal continues to improve 

 in its power of adjustment, though it never completely recovers it. Move- 

 ments of progression are apt to be characterized by stiffness and accom- 

 panied by tremor suggestive of volitional efforts. 



Total removal of the cerebellum is followed by a different train of symp- 

 toms. The extensor muscles apparently preponderate in their action, for 

 the limbs are extended and abducted, the head and neck are retracted, and 



FIG. 260. ATTITUDE IN REPOSE AFTER 

 THE COMPLETE REMOVAL OF THE CERE- 

 BELLUM BUT DURING THE PERIOD OF RES- 

 TORATION OF FUNCTION. (Moral and Doyon, 

 after Thomas.) 



