366 MIDDLE EAR. 



projection called the promontory, above this projection is 

 the foramen ovale or fenestra ovalis, below it is the foramen 

 rotundum or fenestra cochlece. 



The fenestra ovalis is situated directly opposite the mem- 

 brana tyrnpani, is of an oval shape, and leads into the ves- 

 tibule. In the living subject it is closed by a membrane to 

 which the base of the stapes is attached. This membrane, 

 like the tympanic, consists also of three layers, the lining 

 of the tympanum, the lining of the vestibule, and its proper 

 and intermediate layer of fibrous tissue. 



The foramen rotundum leads into the cochlea, and is 

 closed by a similar membrane. 



The promontory corresponds to the first turn of the 

 cochlea, and has upon its surface three grooves, which 

 converge into a common canal, opening on the inferior sur- 

 face of the petrous bone, between the foramen caroticum and 

 foramen lacerum posticum, containing a branch of the glosso- 

 pharyngeal, called Jacobson's nerve. 



Posterior to the fenestra ovalis is a hollow process called 

 the pyramid, containing the small stapedius muscle. 



The anterior wall contains the opening of the Eustachian 

 tube. This tube is a very important structure, and is sit- 

 uated between the tympanum and the pharynx. It is from 

 an inch and a half to two inches in length, passing from 

 the cavity of the tympanum, forward, downward and in- 

 ward, to the posterior nares, above the velum palati, above 

 and behind the lower meatus of the nose, and on a level 

 with the inferior turbinated bone, opening on the sides of 

 the pharynx, in a large, trumpet-like orifice, sufficient to 

 admit the end of the little finger. 



The structure of this tube consists of bone, cartilage, 

 fibrous and mucous tissues. 



The bony portion, about seven lines in length, is situated 

 in the angle between the squamous and petrous bones, and 

 connected with the tympanum. It is attached to the groove 

 between the spinous process of the sphenoid and petrous 

 bones, leading to the root of the internal pterygoid process. 

 Its internal or pharyngeal portion is cartilaginous. The 



