622 TEXT-BOOK OF PHYSIOLOGY 



turbances gradually subside, and in the course of a few months the equilibra- 

 tory power is so far regained that standing and walking at least become 

 possible. In this condition, however, the coordinating power is directly de- 

 pendent on visual impulses, for with the closure of the eyes all the previous 

 motor disturbances at once recur. These and similar facts indicate that the 

 semicircular canals are the peripheral sense-organs from which come the 

 nerve impulses most essential to the excitation of the cerebellar coordina- 

 tive centers in their control of equilibrium and of progression. 



The cerebellum may therefore be regarded as the essential, most highly 

 differentiated portion of the coordinating mechanism concerned in the main- 

 tenance of equilibrium, during both station and progression. The manner 

 in which the cerebellum accomplishes this result is unknown, though it is 

 certain, from the foregoing facts, that its special mode of activity is dependent 

 on the excitatory action of nerve impulses transmitted from a variety of 

 peripheral sense-organs. 



