PHYSIOLOGY OP AUDITION IN MAN. 



191 



mary description of the organs of audition, as far as 

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

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

 any distinct conception of this part, it is necessary to 

 represent it on a larger scale which is done by Fig. 116. 



In this figure the labyrinth 

 is detached from every oth- 

 er P art an d 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. 



All these cavities are surrounded by solid bone, lined 

 with a very delicate membrane called the periosteum, and 

 are filled with a transparent, watery fluid, called the 

 perilymph. The parts marked a , are merely the 

 swellings of the .semi-circular canals at their junction 

 with the vestibule. Within the sac of t hevestibule at 

 the point o, there are found two or three masses of 

 chalky, or calcareous 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 1 What part of the laby- 

 rinth is the vestibule 7 What are the semilunar canals 7 What part is 

 denominated cocklea 1 



