THE PHARYNX. 



153 



Lymph-nodule 

 of pharyngeal 

 tonsil 



Bundles of 

 muscular tissue 

 of constrictors 



stratified squamous, the place of transition being subject to great individual 

 variation. Where covered with the squamous cells, the glands are usually 

 mucous in type. The lower divisions of the pharynx, the oro- and the 

 laryngo-pharynx, are invested with stratified squamous epithelium. 



Lymphoid tissue occurs in great abundance, in certain localities, 

 particularly on the upper posterior pharyngeal wall, causing the mucous 

 membrane to be thrown into elevations. The larger and more constant 

 collections of lymphoid tissue are called ' ' tonsils, ' ' of which the faucial 

 tonsils in the oro-pharynx, the pharyngeal tonsil in the upper part of the 

 naso-pharynx, the tubal tonsils 

 at the openings of the Eusta- 

 chian tubes, and the lingual 

 tonsil on the posterior third of 

 the tongue are examples. 



The faucial tonsils, 

 also called palatine, are two 

 almond-shaped masses of lym- 

 phoid tissue, one on each lat- 

 eral wall of the oro-pharynx, 

 between the palatine pillars. 

 Each tonsil, some 20 mm. 

 long, 15 mm. broad and 10 

 mm. thick, is enclosed by 

 a fibro-elastic capsule, which 

 becomes continuous with the 

 submucous layer where the 

 mucous membrane is adherent 

 to the tonsil, as it is on the 

 free surface. The latter is 

 broken by an uncertain num- 

 ber ( 10-20) of pits of varying 

 size and depth. These depres- 

 sions, or crypts, cut the lym- 

 phoid tissue into irregular 

 tracts, which are still further 

 subdivided by connective tis- 

 sue septa that penetrate from 

 the capsule. The crypts, with 

 their side branches, are com- 

 pletely lined with mucous 

 membrane continued from the 

 adjacent free surface. The 

 tunica propria, however, is thin 

 and so invaded by the lymphocytes that the epithelium is the most conspicu- 

 ous representative of the mucous membrane. Each crypt with its surrounding 

 tract of lymphoid tissue repeats, in its general makeup, the structure of the 

 lingual lymph-follicles already described. The lymphoid mass contains 

 lymph-nodules, with germ-centres, blended together by the more diffuse 

 lymphoid tissue. The entire tonsil is built up by repetition of such structural 

 units. Numbers of lymphocytes wend their way into the subepithelial tissue, 

 which in consequence becomes infiltrated with the lymph-cells, thence pass 

 into the epithelium and, finally, escape into the pit and onto the free surface 

 of the mucous membrane. These cells become the salivary corpuscles. 



Surface 

 epithelium 



FIG. 192 Sagittal section of posterior wall of pharynx of 

 child, showing part of pharyngeal tonsil. X 20. 



