616 



THE SENSES 



tympanic membrane, serving the same mechanical purpose as the vent-hole 

 in a snare or bass drum. The cavity of the tympanum communicates pos- 

 teriorly with air cavities, the mastoid cells, in the mastoid process of the tem- 

 poral bone; but its only opening to the external air is through the Eustachian 

 tube. The cavity of the tympanum is lined with mucous membrane, the 



Recessus epitympanicus 



Body of incus 



Short process of incus 



Ligament of incus 



Chorda tympani nerve 



Pyramid, with tendon 



of stapedius muscle 



jssviing from it 



Superfor'ligament of malleus 

 Head of malleus 



Anterior ligament of malleus 

 -Handle of malleus 



Foot of stapes 



fij^- Tensor tympani muscle 



Osseous part of 

 Eustachian tubfl 





FIG. 432. Left Membrana Tympani and Chain of Tympanic Ossicles (Seen from Inner 

 Aspect). (Cunningham.) 



epithelium of which is ciliated and continuous with that of the pharynx. It 

 contains a chain of small bones, ossicula auditus, which extends from the 

 membrana tympani to the fenestra ovalis. 



The Membrana Tympani. The tympanic membrane is placed in a slant- 

 ing direction at the bottom of the external canal, its plane being at an angle 

 of about forty-five degrees with the lower wall of the canal. It is formed 

 chiefly of a tough and tense fibrous membrane, the edges of which are set 

 in a bony groove. Its outer surface is covered by a continuation of the epithe- 

 lial lining of the auditory canal, its inner surface with part of the mucous 

 membrane of the middle ear. 



The Tympanic Ossicles. The ear bones, or ossicles, are named the 

 malleus, incus, and stapes. The malleus is attached by a long slightly curved 

 process, called its handle, to the membrana tympani, the line of attachment 

 being vertical, including the whole length of the handle, and extending from 

 the upper border to the center of the membrane. The head of the malleus 

 is irregularly rounded; its neck, or the line of boundary between it and the 

 handle, supports a short conical process which receives the insertion of the 

 tensor tympani muscle. The incus, shaped like a bicuspid molar tooth, is 

 articulated by its broader part to the malleus. Of its two fang-like processes, 

 one directed backward has a free end lodged in a depression in the mastoid 

 bone; the other, curved downward and more pointed, articulates by means 



