

THE CEREBELLUM 607 



iost pronounced effects. The head and the anterior part of the body are 

 % once drawn toward the pelvis on the side of the section. A voluntary 

 itfort on the part of the animal causes it to lose all control of its muscles and 

 t.e body is rotated around its longitudinal axis from 40 to 60 times a 

 binute before it comes to rest. According as the lesion is made from be- 

 Jnd or before, the rotation is from or to the side of the section. In time 

 Hiese symptoms subside, though the animal never completely recovers. 



The partial recovery of the power of coordination, observed after removal 

 \: a portion or the whole of the cerebellum, indicates that the centers in the 

 ford, medulla, pons, and cerebrum 

 I'idowed with corresponding 

 Lough less developed power, de- 

 plop compensatory activity and 

 pquire to some extent the capa- 

 bilities of the cerebellum itself 



fig- 259). 



: Clinico-pathologic facts partly 

 brroborate the results of physio- 

 hgic investigations. In various Fm> 259 ._ PROGRESSION AFTER DESTRUCTION 



l)rms of uncomplicated cerebellar F THE VERMIS. (Moral and Doyon, ajter Thomas.) 



fisease, vertigo, tremor on making 



Voluntary efforts, difficulty in maintaining the erect position, unsteadiness 



ii walking, opisthotonos, pleurothotonos, are among the symptoms generally 



ibserved. 



Comparative anatomic investigations reveal a remarkable correspondence 

 letween the development of the cerebellum and the complexity of the move- 

 tents exhibited by animals. In those animals whose movements are corn- 

 flex and require for their performance the cooperation of many groups of 

 nuscles the cerebellum attains a much greater development in reference to 

 he rest of the brain than in animals whose movements are relatively simple 

 h character. This relative increase in the development of the cerebellum 

 3 found in many animals, as the kangaroo, the shark, the swallow, and the 

 iredaceous birds generally. 



The Coordinating Mechanism. Though it is not known how 1 

 erebellum selects and coordinates groups of muscles for the performance 

 ,f any complex movement, it is known that its activity is largely reflex in 

 rigin and excited by impulses which come to it from peripheral organs, 

 his as in other forms of reflex activity the mechanism involves (i) afferc 

 lerves, e.g., cutaneous, muscle, optic, and vestibular, and their related end- 

 ,rgans, tactile corpuscles, muscle spindles, retina, and semicircular cam 

 til indirectly connected with (2) the cerebellar centers; (3 1 efferent nerves 

 ndirectly connected with (4) the general musculature of the body 

 ;tation and progression are directly dependent on the development and 

 ransmission of ffferent impulses from the previously ^"^p^M 

 'sense-organs to the cerebellum. Tactile, muscle, visual, and jabynntlune 

 impressions and sensations not only cooperate in the deve opment and or- 

 ?anization of the motor adjustments necessary to the maintenance ot 



t^ but even after their organization 



ar ^ necessary to the excitation of cerebellar activity The manner in 

 ^th "Soothe development of this capability on the part of the cere- 



