THE LARYNX AND THE EAR 



361 



than three fourths of an inch and its greatest diameter not 

 more than one half of an inch. It is filled with a liquid 

 which at one place is called the perilymph, and at another 

 place the endolymph. It is a double organ, being made up 

 of an outer portion which Ues next to the bone, and which 

 surrounds an inner portion of the same general form. 

 The outer portion is surrounded by a membrane which 

 serves as periosteum to 

 the bone and, at the 

 same time, holds the 

 liquid belonging to this 

 part, called the peri- 

 lymph. The inner 

 portion, called the mem- 

 branous labyrinth, con- 

 sists essentially of a 

 closed membranous sac, 

 which is filled with the 

 endolymph. The audi- 

 tory nerve terminates 



FIG. 152. General form of internal 

 ear. The illustration represents the struc- 

 in this portion of the tures of the internal ear surrounded by a 



internal ear. Three thin la y gr of bone ' ' Vestibule - 2 - Coch ' 



lea. 3 



ovalis. 



Semicircular canals. 

 Fenest ra rotunda. 



4. Fenestra 



distinct divisions of the 



labyrinth have been 



made out, known as the vestibule, the semicircular canals, 



and the cochlea (Fig. 152). 



The Vestibule forms the central portion of the internal 

 ear and is somewhat oval in shape. It is in communication 

 with the middle ear through a small opening in the bone, 

 called fazfenestra ovalis, at which place it is separated 

 from the middle ear only by a thin membrane. Sound 

 waves enter the liquids of the internal ear at this point, 

 the foot of the stapes being attached to the membrane. 



