FUNCTIONS OF THE NERVOUS SYSTEM 307 



other. It has long been regarded as established that its 

 special function is to act as a center not the sole, but the 

 great center for coordination of muscular movement, and 

 especially for that coordination of muscles necessary to 

 maintain the body in a position of equilibrium. This 

 harmonious adjustment of the working of so large a 

 number of muscles requires the action of a large and 

 complicated nervous mechanism, involving the eyes, por- 

 tions of the auditory apparatus, and the apparatus for 

 touch, as well as the muscular sense which tells us what 

 we are doing with our muscles. Sensory impulses from 

 these four sources reach the cerebellum by its peduncles 

 and keep it informed as to the position of the body in 

 space. Then, in order that all the numerous muscles 

 involved may act with regulated strength and in mutual 

 harmony to preserve the equilibrium, the nerve centers 

 in each half of the cerebellum send on afferent impulses 

 to the cerebral hemisphere of the opposite side. There 

 takes place the motor discharge which sends forth the 

 efferent impulse to the muscles. In the process of select- 

 ing the muscles which are to act, and arranging the order 

 and amount of their action, the gray matter of the higher 

 centers, of the basal ganglia, the cerebellum, and the 

 whole of the spinal cord is concerned. 



The cerebellum is also especially involved in the pro- 

 duction of the finer and more delicate movements of the 

 hand. 



448. Functions of the Corpora Quadrigemina and the Crura 

 Cerebri. Of the functions of the crura cerebri, or pedun- 

 cles of the cerebrum, we know little except that they con- 

 duct nervous impulses. If one peduncle is destroyed, the 

 animal moves toward the opposite side, round and round 

 in circles. The corpora quadrigemina, or optic lobes, are the 



