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HANDBOOK OF PHYSIOLOGY. 



ated fibres (constrictors), which are covered by a thin fascia externally, 

 and are lined internally by a strong fascia (pharyngeal aponeurosis), on 

 the inner aspect of which is areolar (submucous) tissue and mucous 

 membrane, continuous with that of the mouth, and, as regards the part 

 concerned in swallowing, is identical with it in general structure. The 

 epithelium of this part of the pharynx, like that of the mouth, is strati- 

 fied and squamous. 



The pharynx is well supplied with mucous glands (fig. 241). 



Between the anterior and posterior arches of the soft palate are sit- 

 uated the Tonsils, one on each side. A tonsil consists of an elevation 

 of the mucous membrane representing 12 to 15 orifices, which lead into 



g^ r ^Epithel. 



Fig. 246. 



Fig. 247. 



Fig. 246. Lingual follicle or crypt, a, involution of mucous membrane with its papillae; b, 

 lymphoid tissues, with several lymphoid sacs. (Frey.) 



Fig. 247. Vertical section through a crypt of the human tonsil. 1, entrance to the crypt ; 2 and 

 3, the framework or adenoid tissue; 4, the inclosing fibrous tissue ; a and b, lymphatic follicles; 5 

 and 6, blood-vessels. (Stohr.) 



crypts or recesses, in the walls of which arc placed nodules of adenoid 

 or lymphoid tissue (fig. 247). These nodules are enveloped in a less 

 dense adenoid tissue which reaches the mucous surface. The surface 

 is covered with stratified squamous epithelium, and the subepithelial or 

 mucous membrane proper may present rudimentary papillae formed of 

 adenoid tissue. The tonsil is bounded by a fibrous capsule (fig. 247, 4). 

 Into the crypts open the ducts of numerous mucous glands. 



The viscid secretion which exudes from the tonsils serves to lubri- 

 cate the bolus of food as it passes them in the second part of the act of 

 deglutition. 



