Chap. XX] INTERNAL AND EXTERNAL SENSES 417 



tached to the base of the anvil. The long process of the anvil is 

 attached to the stapes, and the footpiece of the stapes is attached 

 to the fibrous membrane that is stretched across the oval window. 

 These little bones are held in position, attached to the drum-mem- 

 brane, to each other, and to the membrane of the oval window by 

 minute ligaments and muscles. They are set in motion with every 

 movement of the drum-membrane. Vibrations of the mem- 

 brane are communicated to the hammer, taken up by the an^'il, 



Fig. 194. — Ossicles of the Tympanum, X 4. I, ossicles of the left ear ; 1, 

 malleus; 2, incus; 3, stapes. II, ossicles of the right ear; 1, malleus; 2, long 

 process ; 3, handle ; 4, long process of the incus ; 5, short process of the incus ; 

 6, stapes. (Flint.) 



and transmitted to the stirrup, which rocks in the fenestra ova- 

 lis, and is therefore capable of transmitting to the fluid in the 

 cavity of the labyrinth the impulses which it receives. 



Internal ear. — The internal ear, or labyrinth, receives the ulti- 

 mate terminations of the auditory nerve, and is, therefore, the 

 essential part of the organ of hearing. It consists of a bony 

 labyrinth, which is composed of a series of peculiarly shaped 

 cavities, hollowed out of the petrous portion of the temporal 

 bone, and named from their shape : — 



(a) The vestibule. 



(6) The semicircular canals. 



(c) The cochlea (snail-shell). 

 Within the bony labyrinth is a membranous lab3rrinth, which is 

 composed of a series of sacs, or tubes, fitting more or less closely 

 within the vestibule, semicircular canals, and coclilea. In some 

 2e 



