362 HUMAN ANATOMY. 



Outer wall, formed by the tympanic membrane and the 

 annulus tympanicus surrounding it: 



Iter chorda? posterius, gives entrance to chorda tympani nerve ; 



Iter chordae anterius, or canal of Hugier, gives exit to same; 



Glaserian fissure, above and in front of annulus tympanicus, re- 

 ceives the anterior ligament of the malleus, the long process of the 

 malleus, and the tympanic artery; 



Pouches of the manbrana tt/mpani, are two or three pockets formed 

 by the doubling of the mucous membrane around the chorda tympani 

 nerve. 



Inner wall, separates the tympanum from the labyrinth: 



Fenestra ovalis, an oval window, leading to the vestibule, closed 

 by the membrane to which the base of the stapes is attached ; 



Fenestra rotunda, a round window, leading to the scala tympani, 

 but closed also by a membrane mcmbrana tympani secundaria. 



Promontory, two grooves, marking the first turn of the cochlea, 

 and separating the fenestrse ovalis and rotunda; 



Pyramid, a small conical eminence behind the fenestra ovalis, which 

 contains within it the stapedius muscle, and communicates with the 

 aquaeductus Fallopii. 



Posterior wall: 



Openings of the mastoid cells, three or four in number, connect 

 these sinuses with the tympanum. 



Anterior wall, is a thin plate of bone, which separates the 

 tympanum from the carotid canal. 



Openings of the canal for tensor tympani, lies above and parallel 

 with the canal for the Eustachian tube, and transmits the tensor tym- 

 pani muscle; 



Opening of Eustachian tube, the larger of the two, is separated 

 from the former by a thin plate of bone, the proccssus cocJilcariformis. 



The tympanum is divided into two parts the attic of the 

 tympanum and the atrium. The former is situated on a plane 

 directly above the atrium, and is bounded above by the tegmen, 

 externally by auditory plate, and internally by prominence of the 

 tympanum. On the outer part of the attic is a smooth surface 

 called the scute (Leidy). 



THE EUSTACHIAN TUBE is an osseo-cartilaginous canal, one 

 and one-half to two inches in length, extending from the tym- 

 panum to the pharynx. 



It is about one-third osseous and two-thirds cartilaginous, 

 and lined with ciliated epithelium continuous with the pharynx 



