THE MIDDLE EAR. 



1503 



persists. It is this cartilage, covered by the cushion of mucous membrane, that 

 confers the characteristic Gothic arch contour to the lower opening, the osteum 

 pharyngeum, of the tube. 



The Mucous Membrane of the Eustachian Tube. The Eustachian 

 tube is lined throughout its length with mucous membrane, which differs some- 

 what in the cartilaginous and osseous portions. That in the former resembles the 

 mucous membrane of the naso-pharynx, with which it is directly continuous, whilst 

 that of the osseous division resembles, to some extent, the mucous membrane of the 

 tympanic cavity. The epithelium of both divisions consists of the ciliated stratified 

 columnar type, with some goblet cells, but the cells in the pharyngeal division, 

 especially in the lower part, are taller than those of the tympanic portion, which are 

 low cuboidal. 



In the tympanic portion the mucous membrane is closely united with the perios- 

 teum and contains very few mucous glands and little or no adenoid tissue. In the 

 cartilaginous division, on the contrary, the epithelium overlies a layer of adenoid 



FIG. 1262. 



Lateral lamina 



".'' i . \- _Mesial lamina of cartilage 



.'.'.' ' 'of tube 



Oblique muscle-fibres ^BHHBrr -'} ' 



Lumen of tube 



-Glands 



'. 



Tensor palati (dilator tubae)- 



Levator palati-- 

 Transverse section of cartilaginous Eustachian tube. X 7- 



tissue, often called the tubal tonsil. This tissue is especially abundant in children, 

 and beneath it are found numerous mucous glands which open on the free surface of 

 the tube. These glands extend nearly to the perichondrium and sometimes can be 

 traced even through the fissures in the cartilage into the surrounding connective tissue. 

 A considerable amount of adipose tissue often occupies the submucosa of the lower 

 and lateral walls. The submucous layer is well developed in the cartilaginous 

 division of the tube, particularly in the outer membranous wall. It consists of 

 loosely arranged fibro-elastic tissue, which supports the mucous glands and the 

 larger vessels and nerves. 



The muscles of the Eustachian tube are the levator and the tensor palati, the 

 contractions of which not only affect the palate, but also produce changes in the 

 position of the floor and in the lumen of the tube. These muscles are described in 

 connection with the palate ('page 1570), suffice it here to note their close relations to 

 the Eustachian tube, beneath and to the inner side of which the levator lies, and to the 

 outer side of which the tensor extends. By reason of the intimate attachment which 

 both muscles have to the cartilage of the tube, since both take partial origin from this 

 structure, contraction of their fibres tend to draw apart the walls of the canal and they 

 thus serve as dilators. Such action is particularly true of the tensor palati, many of 



