THE MIDDLE EAR. 



479 



ception of the articular cartilages, rest on the periosteum (Riidin- 

 ger, 70). 



Thefexestra rotunda (fenestra cochleae) is closed by the secon- 

 dary or inner tympanic membrane, a connective-tissue membrane 

 containing vessels and nerves, the outer wall of which is covered by 

 ciliated epithelium, the inner (the surface toward the scala tympani) 

 by flattened endothelial cells. 



In the antrum and mastoid cells, the mucosa of the mucous 

 membrane is immovably fixed to the periosteum. The epithelium 

 is of the simple squamous variety and is nonciliated. 



Portion of Eusta- 

 chian tube free 'WlfS-;* 

 from glands. 



Cartilage. 



KnHi Mucosa of the 



pharynx. 



Glands. 



Glands. ,-_-_---- 



Fig. 367. Cross-section of the Eustachian tube with its surrounding parts; X I2 (from 

 a preparation by Professor Riidinger). 



The mucous membrane of the osseous portion of the Eustachian 

 tube is very thin, and its mucosa is intimately connected with the 

 periosteum. Its epithelium is of the simple pseudostratified ciliated 

 variety, having two strata of nuclei. There are no glands. The 

 mucous membrane of the cartilaginous portion of the Eustachian 

 tube is thicker, and its epithelium, which is of the stratified ciliated 

 variety, is higher, and often contains goblet-cells. Lymphoid tissue 

 may be demonstrated in the mucosa of this portion, and occasion- 

 ally structures resembling lymph-nodules are found, especially in the 

 vicinity of the pharyngeal opening of the tube. In the cartilaginous 

 portion of the, tube are mucous glands, which are particularly 



