236 HAND-BOOK OF PHYSIOLOGY. 



The materials which they have incorporated with themselves are almost 

 at once given up again, in the form of a fluid (secretion), which escapes 

 from the ducts of the gland; and the cells, themselves, undergo disinte- 

 gration, again to be renewed, in the intervals of the active exercise of 

 their functions. The source whence the cells obtain the materials of 

 their secretion, is the blood, or, to speak more accurately, the plasma, 

 which is filtered off from the circulating blood into the interstices of the 

 glands as of all living textures. 



THE PHARYNX. 



That portion of the alimentary canal which intervenes between the 

 mouth and the oesophagus is termed the Pharynx (Fig. 165). It will 

 suffice here to mention that it is constructed of a 

 series of three muscles with striated fibres (constrict- 

 ors), which are covered by a thin fascia externally, 

 and are lined internally by a strong fascia (pharyn- 

 geal 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 swalloAving, is identical with 

 i^ i n general structure. The epithelium of this part 

 of the Pharynx, like that of the mouth, is stratified 



brane with its papillae; nr\(\ cminrnrmss 

 6, lymphoid tissue, with an US ' 



(Key 8 ) lymphoid sacs - The pharynx is well supplied with mucous glands 

 (Fig. 174). 



The Tonsils. Between the anterior and posterior arches of the soft 

 palate are situated the Tonsils, one on each side. A tonsil consists of an 

 elevation of 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 lymphoid tissue (Fig. 173). 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 papillse formed of 

 adenoid tissue. The tonsil is bounded by a fibrous capsule (Fig. 173, e). 

 Into the crypts open a number of ducts of mucous glands. 



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 degluti- 

 tion. 



THE (ESOPHAGUS OR GULLET. 



The (Esophagus or Gullet (Fig. 165), 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. 



