VISCERAL ANATOMY. 1 59 



9. Scuio-auricularis internus. 

 Origin. — Beneath sciitiform. 

 Insertion. — Base of concha. 



Action. — Antagonizes No. 3. Turns ear outward and backward. 



10. Mastoido-auricularis. 



Origin. — Margin of auditory meatus. 

 Insertion. — Into base of concha. 

 Action. — Constricts meatus. 



Skin. — Thin, vascular, and covered with fine hairs. 



EXTERNAL AUDITORY CANAL. 



This is a short canal lodged in the petrous portion of the tem- 

 poral bone, commencing at the external meatus and ending at the 

 middle ear, being shut off from that cavity by the membrana 

 tympani. The canal is Hned with thin skin which contains a num- 

 ber of ceruminous glands which secrete cerumen or wax. 



MIDDLE EAR OR TYMPANUM. 



The tympanum is a cavity situated in the interior of the tem- 

 poral bone at the junction of its mastoid and petrous portions, 

 communicating with the pharynx by a canal lined with mucous 

 membrane, the FAistachian tube. It has an external wall formed 

 by the membrana tympani, an internal, shutting it off from the in- 

 ternal ear, showing two openings, the fenestra ovalis diXidi fenestra 

 rotunda, separated by an elevation, the pro77iontory, and a circum- 

 ference, which shows the openings of many mastoid cells. It is 

 lined with mucous membrane continuous with that of the pharynx, 

 and covered with pavement epithelium. 



The Membrana Tympani shuts off the external meatus from 

 the tympanum, is concave externally, convex internally, set 

 strongly in a bony depression and adherent internally to the han- 

 dle of the malleus. It consists of three layers, a middle, fibrous 

 and muscular, an external of skin, and an internal of mucous 

 membrane. 



The Fenestra Ovalis, lying in front of the promontory, is oval 

 in shape, closed by the base of the stapes, and communicates with 

 the vestibule. 



The Fenestra Rotunda communicates with the scala tympani 

 and is closed in by a membrane. 



