AUDITORY APPARATUS IN MAN. 



187 



Fig. 116. 



inary description of the organs of audition, as far as the 

 labyrinth, which in Fig. 114, is marked v, s, k, and is 

 there drawn of the natural size. But in order to give 

 any distinct conception of this part, it is necessary to rep- 

 resent it on a large scale, which is done by Fig. 116. 

 In this figure, the labyrinth 

 is detached from every other 

 part, and separated from the 

 solid bone in which it is 

 embedded. It consists of a 

 middle portion called the 

 vestibule, v, from which, on 

 its upper and posterior side, 

 proceed the three tubes, x, y, 

 z, called from their shapes, 

 the semi-circular canals ; 

 while the lower side of the 

 vestibule terminates in a spi- 

 ral canal, resembling in ap- 

 pearance, or rather in form, 

 the shell of a snail, k, and 

 on that account is denomi- 

 nated the cochlea. 



580. All these cavities are surrounded by solid bone, 

 lined with a very delicate membrane, called the perioste- 

 um, and are filled with a transparent, watery fluid, called 

 the perilymph. The parts marked a, a, are merely the 

 swellings of the semi-circular canals at their junction with 

 the vestibule. Within the sac of the vestibule at the point 

 o, there are found two or three masses of chalky, or cal- 

 careous matter, suspended in the fluid by the intervention 

 of some nervous filaments, proceeding from the auditory 

 nerve. These exist in the ears of all the mammalia, and 

 therefore undoubtedly perform some important office, but 

 of what kind is unknown. They are also found in aquatic 

 animals, and of a larger size, and greater hardness, than 

 in others. 



Where is the labyrinth of the ear situated ? What part of the labyrinth 

 is the vestibule ? What are the semi-circular canals f What part is de- 

 nominated cochlea ? 



