98 INNERVATION. [CHAP. xviu. 



Miiller, "must be regarded as a surface upon which all the fibres of 

 the cochlear nerve are spread out, so as to be nearly simultaneously 

 exposed to the impulse of the sonorous undulation, and simulta- 

 neously thrown into the maximum state of condensation, and again 

 into the maximum state of rarefaction. " " This spreading out of 

 the nerve fibres upon the lamina spiralis, insures a more complete 

 participation of the fibres in the impulses communicated by the solid 

 parts of the cochlea." Moreover, " the intensity with which sono- 

 rous undulations are communicated to a body, is proportionate to the 

 extent of surface over which they can act on it. Thus when a 

 sound is excited in water, and is conducted to the stopped ear by 

 means of a rod, the intensity of the sound heard increases with the 

 depth to which the rod is immersed in the water, or with the ex- 

 tent in which it is in contact with the surface of the water." * 



The fluid in the scalse of the cochlea, with the helicotrema or 

 orifice of communication must facilitate the vibrations of the lamina 

 spiralis, and we have already assigned to the cochlearis muscle a 

 protective use to the cochlear nerves. 



The Otoliths. The earthly particles, which, either as pulverulent 

 masses, or as hard porcelainous stones, are connected with the nerves 

 of the membranous labyrinth, must reinforce the sonorous undula^ 

 tions, and communicate to the membranous labyrinth and its nerves 

 vibratory impulses of greater intensity than the perilymph alone 

 could impart. In illustration of this, Miiller mentions that sonorous 

 undulations in water are not perceived by the hand itself immersed 

 in the water, but are felt distinctly through the medium of a rod 

 held in the hand. The experiment of Camper is also illustrative. 

 Fill a bladder with water and place a stone or some other hard body 

 in it. The slightest impulse communicated to the bladder disturbs 

 the stone, which consequently produces a greater impression on the 

 hand by which the bladder is supported. 



The Semicircular Canals. There is nothing known of the 

 function of the semicircular canals. Yet their almost constant 

 existence, and nearly constant number evince their physiological 

 importance. In most cases of congenital deafness they are found 

 defective. 



Their constancy, in the higher animals, of number and of position, 

 which is such that they correspond to the three dimensions of a cube, 

 its length, breadth, and depth, suggested to Autenrieth and Kerner 

 the opinion that they are the parts concerned in conveying a know- 



* Miiller's Physiology, by Baly, vol. ii. p. 1294. Dr. Young regarded 

 cochlea, as a micrometer of sound. 



the 



