THE SENSE OF HEARING. 



753 



lembrana t} r mpani to the oval window. In number they are three: 

 ie malleus, or mallet ; the incus, or anvil ; and the stapes, or stirrup. 

 The three ossicles form a chain suspended across the cavity of the 

 tympanum. The handle of the malleus is inserted into the tym- 

 panic membrane ; the base of the stirrup is applied to the oval win- 

 dow. Between these two ossicles is suspended the incus. The 

 ossicles have joints which are lined with synovial membrane; there 

 are present suitable ligaments. 



The mucous membrane of the tympanum is very thin, and either 

 or rose-colored. It envelops the chain of ossicles. 



Fig. 310. Scheme of the Organ of Hearing. (LANDOis.) 



AG, External auditory meatiis. T, Tympanic membrane. K, Malleus with 

 its head (h), short process (fcf), and handle (m). a, Incus, with its short 

 process (x) and long process; the latter is united to the stapes (.9). P, Middle 

 ear. o, Oval window, r, Round window, x, Beginning of the lamina spiralis 

 of the cochlea, pt, Its scala tympani. vt, Its scala vestibuli. V, Vestibule. 

 8, Saccule. U, Tubercle. H, Semicircular canals. TE, Eustachian tube. The 

 long arrow indicates the line of traction of the tensor tympani; the short 

 curved one that of the stapedius. 



The Eustachian tube is composed of a bony and a cartilaginous 

 irt. The canal opens at the anterior upper part of the tympanum; 

 its pharyngeal orifice is situated ten millimeters behind the posterior 

 extremity of the nasal fossa. 



THE BONY LABYRINTH, OR INTERNAL EAR. This structure is 

 ibedded within the substance of the petrous portion of the tem- 

 1 bone. Its long axis lies in a position parallel with that of the 

 me. The labyrinth is composed of three portions: vestibule, semi- 

 ircular canals, and cochlea. 



