FUNCTIONS OF THE CEREBELLUxM 523 



When describing the arrangements of the internal ear, 

 it was stated that the semicircular canals have functions 

 other than that of hearing. Now the auditory nerve 

 consists of two quite distinct parts, the cochlear nerve, 

 which is distributed to the cochlea, .and the vestibular 

 nerve, which is distributed to the vestibule, the utricle, 

 saccule, and semicircular canals. The.se two nerves, the 

 axons of which originate in the ear, terminate in connection 

 with groups of cells lying in the spinal bulb, and the 

 group of cells as.sociated with the vestibular nerve is 

 directly connected by a strand of fibres with the cerebellum. 

 Thus there is a path by which afferent (sensory) impulses 

 from the semicircular canals may directly reach the 

 cerebellum and there be turned to account in the co- 

 ordination of movements. Bearing this in mind, it is not 

 surprising to lind that the semicircular canals play a 

 very important part in the guidance of co-ordinated 

 movement. 



The semicircular canals lie in three planes at right 

 angles to each other (p. 392). When any one of the canals 

 is experimentally injured, the animal executes a series of 

 oscillatory movements of the head, which are, broadly 

 speaking, in the plane of that canal. When all three 

 canals are injured, the animal is thrown into continuous 

 movements of tlie most varied and oft«n extraordinary 

 kind, and has lost all power of balancing itself in a 

 normal way. Not infrequently in man these canals 

 undergo injury as the result of disease, and in this case 

 the feelings experienced by the patient are those of ex- 

 treme giddiness, and an inability to balance the body, 

 while the symptoms exhibited to an onlooker are those of 

 a want of co-ordination in the execution of movements. 

 Thus there is no doubt that the semicircular canals are 

 of very great importance as organs such that impulses 

 arising in them, enable us to maintain oir bodily 

 equilibrium, and there are reasons for thinking that the 

 utiicle and saccule also have a very similar function. 



