690 



THE SENSE OF HEARING. 



also, in some degree, the power of conducting sounds in 

 the direction of their curved cavities more easily than the 

 sounds are carried off by the surrounding hard parts in 

 the original direction of the undulations, though this con- 

 ducting power is in them much less perfect than in tubes 

 containing air. 



Admitting that they have these powers, the increased 

 intensity of the sonorous vibrations thus attained will be 

 of advantage in acting on the auditory nerve where it is 

 expanded in the ampulla? of the canals, and in the utri- 

 culus. Where the membranous canals are in contact with 

 the solid parietes of the tubes, this action must be much 

 more intense. But the membranous semicircular canals 

 must have a function independent of the surrounding hard 

 parts; for in the Petromyzon they are not separately 

 enclosed in solid substance, but lie in one common cavity 

 with the utriculus. 



The crystalline pulverulent masses in the labyrinth would 

 reinforce the sonorous vibrations by their resonance, even 

 if they did not actually touch the membranes upon which 

 the nerves are expanded; but, inasmuch as these bodies 

 lie in contact with the membranous parts of the labyrinth, 

 and the vestibular nerve-fibres are imbedded in them, they 

 communicate to these membranes and the nerves vibratory 

 impulses of greater intensity than the fluid of the labyrinth 

 can impart. This appears to be the office of the otoconia. 

 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 fine 

 hair-like prolongations from the epithelial cells of the 

 ampullso have, probably, the same function. 



The cochlea seems to be constructed for the spreading out 

 of the nerve-fibres over a wide extent of surface, upon a 

 solid lamina which communicates with the solid walls of 

 the labyrinth and cranium, at the same time that it is in 

 contact with the fluid of the labyrinth, and which, besides 



