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AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



13 



the bottom and anterior edge of the concha to the membrana tympani, or 



tympanic membrane. Starting 

 from the bottom of the concha, 

 the general direction of the audi- 

 tory canal is first obliquely up- 

 ward and backward for about, 

 half an inch, and then inward 

 and forward. Therefore, to look 

 into the ear or to introduce the 

 aural speculum the canal must be 

 straightened by pulling the pinna 

 upward and backward. The 

 canal- wall is cartilaginous and 

 movable for about half an inch 

 from the exterior, but is osseous 

 for the rest of its extent; it is 

 lined by a reflexion of thin skin, 

 on whose surface, in the cartilag- 

 inous part of the canal, open the 



FIG. 267. -Tympanum of left ear, with ossicles in situ ducts of numerous SebaCCOUS and 



(after Morris) : 1, suspensory ligament of malleus ; 2, head pprnminrmQ o-lnnrlc 

 of malleus ; 3, epitympanic region ; 4, external ligament 



of malleus; 5, processus longus of incus; 6, base of stapes; Tympanum. The middle ear, 



7, processus brevis of malleus; 8, head of stapes; 9, os /-m- o/i/> r/*r\ 



orWc^ar e ;10,manubrium;ll,Eustachiantube;12,exter- r tympanum (FlgS. 266, 267), IS 



nal auditory meatus; 13, membrana tympani; 14, lower shut off from the auditory canal 



part of tympanum. , , 



by the tympanic membrane. It 



is an air-holding cavity of irregular shape in the petrous bone, and it is broader 

 behind and above than it is below and 

 in front. Posteriorly it is in open com- 

 munication with the complex system of 

 air-cavities in the mastoid bone known 

 as the mastoid antrum and the mastoid 

 cells. Anteriorly it is continuous with the 

 pharynx through the Eustachian tube. 

 The inner wall slants somewhat outward 

 from top to bottom, and it is formed 

 chiefly by part of the bony envelope of 

 the internal ear. The surface of this wall 

 is pierced by two apertures, the fenestra 

 ovalis, or oval window, and the fenestra 



rotunda, or round window, leading into FIG. 268.-Otoscopic view of left membrana 



the cavity of the bony labyrinth; in life ??l pa ( M q orris ^ l > membrana flaccid a ; 2,2', 



i f . j i . folds boundm g th e former ; 3, reflection from 



each tenestra IS Covered by a thin sheet processus brevis of malleus ; 4, processus lon- 



of membrane, and the foot of the stapes T" f incus . (occasionally seen): 5 ' mem - 



. MI P^ brana tympani ; 6, umbo and end of manu- 



is fastened by a hgamentous fringe in the brium; 7, pyramid of light. 



oval window. The outer wall of the middle ear is made up of the tympanic 



