132 CONSCIOUS NERVOUS OPERATIONS 



Within the swollen ends of the semicircular canals, and 

 upon the walls of the utricle and the saccule, are project- 

 ing ridges composed of especially modified cells of the 

 lining, between which are spindle-shaped auditory cells 

 from which project auditory hairs into the fluid. At- 

 tached to these thickened disks, or ridges, are minute hard 

 particles, called otoliths, which serve to increase the effect 

 of the vibrations. The auditory vibrations in the fluid 

 and in the membranous walls of the labyrinth reach the 

 auditory hairs and give, according to the opinions of some 

 authors, the sensation of sound, or mere noise. A branch 

 of the vestibular division of the auditory nerve is distrib- 

 uted to the semicircular canals, and when its ends are 

 affected by the vibrations in the fluids of the labyrinth 

 there result, as is now believed, sensations other than 

 perception of sound. 



178. The same vibrations pass at the same time up the 

 channel of the cochlea from below, affecting on their way 

 the walls of the membranous cochlea, and throwing into 

 vibration the fluid which they inclose. By the vibrations 

 of the fluid and the membrane the nerve endings in the 

 organ of Corti are acted upon in such a way as to give 

 rise to auditory impulses, resulting in perception of sound 

 quality musical notes, harmony, etc. The cochlea alone 

 is now regarded as concerned with hearing, other parts 

 of the inner ear with equilibrium, etc. Sound waves may 

 also reach the auditory cells by transmission through the 

 bones of the head, as when one- hears the ticking of a 

 watch held between the teeth. 



The auditory stimulus passes from the auditory cells 

 by the minute nerve fibers to that branch of the eighth 

 cranial, or auditory nerve, which passes through the coch- 

 lea and into the medulla obloiigata (Fig. 78), whence 



