242 HANDBOOK OF PHYSIOLOGY. 



the mucous membrane presenting 12 to 15 orifices, which lead into crypts 

 or recesses, in the walls of which are placed nodules of adenoid or lym- 

 phoid tissue (Fig. 181). 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. 181, e). Into 

 the crypts open the ducts of numerous mucous glands. 



FIG. 181. Vertical section through a crypt of the human tonsil, a., entrance to the crypt" 

 which is divided below by the elevation which does not quite reach the surface; 6, stratified epithe 

 lium; c, masses of adenoid tissue ; d, mucous glands cut across; e, fibrous capsule. Semidiagram 

 matic. (V. D. Harris.) 



The viscid secretion which exudes from the tonsils serves to lubricate 

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

 tition. 



THE (ESOPHAGUS OR GULLET. 



The (Esophagus or G-ullet (Fig. 164), the narrowest portion of the 

 alimentary canal, is a muscular and mucous tube, nine or ten inches in 

 length, which extends from the lower end of the pharynx to the cardiac 

 orifice of the stomach. 



Structure. The oesophagus is made up of three coats viz., the outer, 

 muscular; the middle, submucous; and the inner, mucous. The mus- 

 cular coat (Fig. 183, g and i), is covered externally by a varying amount 

 of loose fibrous tissue. It is composed of two layers of fibres, the outer 

 being arranged longitudinally, and the inner circularly. At the upper 

 part of the oesophagus this coat is made up principally of striated muscle 

 fibres, as they are continuous with the constrictor muscles of the pharynx; 

 but lower down the unstriated fibres become more and more numerous, 



