THE EAR, HEARING, TASTE AND SMELL 



231 



by the drum membrane to the handle of the malleus are com- 

 municated with diminished range, but increased power, to the base 

 of the stapes. 



Ordinarily sound-waves reach the labyrinth through the tym- 

 panum, but they may also be transmitted through the bones of the 

 head; if the handle of a vibrating tuning-fork be placed on the top 

 of the head, the sounds heard by the person experimented upon 

 seem to have their origin inside his own cranium. Similarly when a 

 vibrating body is held between the teeth, sound reaches the end 

 organs of the auditory nerve through the skull-bones; and persons 

 who are deaf from disease or injury of the tympanum can thus be 

 made to hear, as with the audiphone. Of course if deafness be due 



A 



Co 



FIG. 71. Casts of the bony labyrinth. A, left labyrinth seen from the outer 

 side; B, right labyrinth from the inner side; C, left labyrinth from above; Fc, round 

 foramen; Fv, oval foramen; h, horizontal semicircular canal; ha, its ampulla; 

 Vaa, ampulla of anterior vertical semicircular canal; Vpa, ampulla of posterior 

 vertical semicircular canal; Vc, conjoined portion of the two vertical canals. 



to disease of the proper nervous auditory apparatus no device can 

 make the person hear. 



The Internal Ear. The labyrinth consists primarily of cham- 

 bers and tubes hollowed out in the temporal bone and inclosed by 

 it on all sides, except for the oval and round foramina on its ex- 

 terior, and certain apertures on its inner side by which blood- 

 vessels and branches of the auditory nerve enter; during life all 

 these are closed water-tight in one way or another. Lying in the 

 bony labyrinth thus constituted, are membranous parts, of the 

 same general form but smaller, so that between the two a space is 

 left; this is filled with a watery fluid, called the perilymph; and the 

 membranous internal ear is filled by a similar liquid, the endolymph. 



The Bony Labyrinth. The bony labyrinth is described in three 

 portions, the vestibule, the semicircular canals, and the cochlea; 



