THE SENSE OF HEARING. 



679 



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

 337, 338. 



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

 of which the latter is atttached 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. 



, 339). It arises from the car- 



7 tilaginous portion of the Eusta- 



W h / / 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. 337 . TYMPANIC MEMBRANE AND THE AUDI- 

 TORY OSSICLES (LEFT) SEEN FROM WITHIN, i. e., 

 FROM THE TYMPANIC CAVITY. M. Manubrium 

 or handle of the malleus. T. Insertion of the 

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

 the malleus, a. Jncus, with the short (K) and the 

 long (/) process. 5. Plate of the stapes. Ax, 

 Ax, is the common axis of rotation of the auditory 

 ossicles. S 1 . The pinion-wheel arrangement be- 

 tween the malleus and incus. (Landois.) 



FIG. 338. 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 foramen 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 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 portion, 

 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 semicir- 



