THE SENSE O"F HEARING 



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. 



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 tympam. 



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



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



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



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



supported by a ligament attached to the shrot process of the incus am 



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 (Tig. 



320). It arises from the car- 

 s' tilaginous portion of the Eusta- 

 chian tube and the adjacent 

 portion of the sphenoid bone. 

 From thisTorigin it passes nearly 

 horizontally backward to the 

 tympanic cavity; just opposite 



FlG - g TYMPANIC MEMBRANE AND THE AUDI- 

 TOR OSSICLES (LEFT) SEEN FROM WITHIN, ., 

 FROM THE TYMPANIC CAVITY. M. Manubnum 

 or handle of the malleus. T. Insertion of the 

 "ensor tvmpani. h. Head. IF. Long process of 

 the malleusf a. Incus, with the short (K) and t 

 ong ( process. 5. Plate of the stapes A*, 

 JS^s the common axis of rotation of the auditory 

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

 tween the malleus and incus. (Landois.) 



TIG. 319. 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.) 



inserted into the handle of ^ 



its point of articulation with the incus . g located 



The Internal Ear. > ron s ists { an osseous and a 



taS within the former. 



into vestibule> se r 



the petrous portion of 



'e Vllt-The vestibule is a small, triangular-shaped cavity between 



