368 



NORMAL HISTOLOGY. 



The posterior wall of the pharyngeal portion is formed by a plate of 

 cartilage, the upper margin of which is curled outwards upon itself to foi .n a 

 gutter, which appears as a hook on transverse section. The interval bet\\ '?en 

 the margins of this cartilaginous groove is rilled with strong fibrous tissue, 

 thus completing the canal. At birth the cartilage is entirely of the hyaline 

 variety, but later this is more or less extensively replaced by fibrocartilage, 

 except in the upper part where the hyaline cartilage persists. 



The mucous membrane of the Eustachian tube lines the tube through- 

 out its length, but differs somewhat in the cartilaginous and osseous portions. 

 That in the former resembles the mucous membrane of the naso-pharynx, 



Lateral lamina 



ObKque muscle-fibres 



Lumen of tube 



Tensor palati 



Cartilage of tube 



lands 



Levator palati 

 



FIG. 417. Section across cartilaginous part of Eustachian tube. X 7- 



with which it is directly continuous, while that of the osseous division resem- 

 bles, to some extent, the mucous membrane of the tympanic cavity. The 

 epithelium of both divisions is of the ciliated stratified columnar type, with 

 some goblet-cells. 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 periosteum and contains very few mucous glands and little or no 

 lymphoid tissue. In the cartilaginous division, on the contrary, the epithe- 

 lium overlies a layer of such 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 fibre-elastic tissue, which supports the mucous 

 glands and the larger vessels and nerves. 



