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TEXT-BOOK OF PHYSIOLOGY. 



FIG. 311. AUDI- 

 TORY OSSICLES. 

 i. Head of 

 malleus. 2. Pro- 

 cessus brevis. 3. 

 Processus graci- 

 lis. 4. Manubri- 

 um. 5. Long pro- 

 cess of incus. 6. 

 Articulation be- 

 tween incus and 

 stapes. 7. Stapes. 

 (Sappey.) 



a right angle over the processus cochleariformis and then passes 

 outward across the tympanic cavity to be inserted into the handle 

 of the malleus near the neck. 



The stapedius muscle emerges from the cavity 

 of a pyramid of bone which projects from the 

 posterior wall of the tympanum. Its tendon 

 passes forward to be inserted into the neck of 

 the stapes bone near its point of articulation with 

 the incus. 



The internal ear, or labyrinth, is located 

 within the petrous portion of the temporal bone. 

 It consists of an osseous and a membranous por- 

 tion, the latter contained within the former. 



The osseous labyrinth is subdivided into 

 vestibule, semicircular canals, and cochlea. 



The vestibule is a small, triangular- shaped 

 cavity between the semicircular canals and the 

 cochlea. It is separated from the cavity of the 

 middle ear by an osseous partition which pre- 

 sents near its center an oval opening, the foramen 

 ovale. In the living condition this opening is 

 closed by the base of the stapes bone, which is 

 held in position by an annular ligament. The inner wall presents 

 a number of openings for the passage of nerve-fibers (Fig. 313). 



The semicircular canals are three in number, a superior vertical, 

 an inferior vertical, and a horizontal, 

 each of which opens by two orifices into 

 the cavity of the vestibule, with the ex- 

 ception of the two vertical, which unite 

 at one extremity and then open by a 

 single orifice. Each canal near its vesti- 

 bular orifice is enlarged to almost twice 

 the size of the rest of the canal, forming 

 what is known as the ampulla. 



The cochlea, the anterior portion of 

 the labyrinth, is a gradually tapering 

 canal, about 35 mm. in length, wound 

 spirally two and a half times around a 

 central bony axis, the modiolus. The 

 cavity of the cochlea is partially subdi- 

 vided into two cavities by a thin spiral 

 plate of bone which projects from the inner wall, known as the 

 lamina osseous spiralis. In the natural condition this partition is 

 completed by a connective-tissue membrane, so that the two passages 

 are completely separated from each other. The upper passage or 



FIG. 312. M, THE TENSOR 

 TYMPANI MUSCLE THE 

 EUSTACHIAN TUBE (LEFT). 

 (Landois.) 



