130 CONSCIOUS NERVOUS OPERATIONS 



canal, is closed at its apex, but opens near its base into the 

 saccule. In the cochlear canal is situated the most deli- 

 cate part of the ear, the organ of Corti. 



174. Fluids of the Labyrinth. The bony canal of the 

 inner ear is lined with a fine membrane which secretes a 

 thin fluid, filling all the spaces of the chamber. The 

 closed sac of the membranous labyrinth also secretes a 

 fluid similar in composition, but containing less solid 

 matter. When the membrane of the tympanum is 

 thrown into vibration, the movement is communicated to 

 the fluid filling the bony labyrinth, and then through 

 the thin wall of the membranous labyrinth to the fluid 

 inclosed, and so to the terminations of the auditory nerve. 



175. The Auditory Nerve and the End Organs for Hearing. 

 The eighth cranial nerve arises by two roots in certain 

 nerve centers of the medulla oblongata. Its two divi- 

 sions enter the labyrinth between the base of the cochlea 

 and the vestibule. One division, having several branches, 

 goes to the vestibule and semicircular canals ; the other 

 passes up through a channel in the bony axis of the coch- 

 lea, giving forth fibers on its way to the bony shelf 

 described above. These pass through, or come into rela- 

 tion with the spiral ganglion and reach the organ of Corti. 



176. The Organ of Corti (Fig. 77), within the mem- 

 branous cochlea, is understood to contain the end organs 

 for the discrimination of degrees, variations, and qualities 

 of sound. It is composed of the rods of Corti with adja- 

 cent hair cells and supporting parts. The rods are pillar- 

 like cells attached by an expanded foot, or base, to one of 

 the membranes of the cochlea and ending in a swelling 

 called the head. 



The pillars are arranged in pairs, of which there are 

 from three thousand to five thousand, separated at their 



