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TEXT-BOOK OF PHYSIOLOGY 



another at their extremities. These bones are known as the malleus, incus, 

 and stapes. The form and arrangement of these bones are shown in Figs. 

 315, 316. 



The malleus, or hammer bone, consists of a head, neck, and handle, 

 of which the latter is attached to the inner surface of the membrana tympani. 

 The incus or anvil bone presents a concave articular surface which receives 

 the head of the malleus. The stapes, or stirrup bone, articulates externally 

 with the long process of the incus, and internally, by its oval base, with the 

 edges of an oval opening, the foramen ovale. The entire chain is partially 

 supported by a ligament attached to the short process of the incus and 

 to the walls of the tympanic cavity. 



The Tensor Tympani Muscle. This is a delicate muscle, about 15 mm. 

 in length, situated in a narrow groove just above the Eustachian tube (Fig. 



317). It arises from the car- 

 tilaginous portion of the Eusta- 

 chian tube and the adjacent 

 portion of the sphenoid bone. 

 From this origin it passes nearly 

 horizontally backward to the 

 tympanic cavity; just opposite 



FIG. 315. TYMPANIC MEMBRANE AND THE 

 AUDITORY OSSICLES (LEFT) SEEN FROM WITHIN, 

 i.e., FROM THE TYMPANIC CAVITY. M. Manu- 

 brium or handle of the malleus. T. Insertion of 

 the tensor tympani. h. Head. IF. Long process 

 of the malleus, a. Incus, with the shortj(-K) and 

 the long (/) process. S. Plate of the stapes. Ax, 

 Ax, is the common axis of rotation of the audi- 

 tory ossicles. 5 l . The pinion-wheel arrangement 

 between the malleus and incus. (Landois.) 



FIG. 316. AUDI- 

 TORY OSSICLES, i. 

 Head of malleus. 2. 

 Processus brevis. 3. 

 Processus gracilis. 

 4. Manubrium. 5. 

 Long process of in- 

 cus. 6. Articulation 

 between incus and 

 stapes. 7. Stapes. 

 (Sappey.) 



the ioramen ovale its tendon bends at 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. 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. The internal ear, or labyrinth, is located within 

 the petrous portion of the temporal bone. It consists of an osseous and a 

 membranous portion of which the latter is contained within the former. 



The osseous labyrinth is subdivided into vestibule, semicircular 

 canals, and cochlea. 



The Vestibule. The vestibule is a small, triangular-shaped cavity between 



