1 68 HISTOLOGY. 



less basement membrane beneath the epithelium is called the membrana 

 propria. The epithelium, membrana propria, and tunica propria together 

 form the mucous membrane. Beneath it, and sometimes not clearly sepa- 

 rable from the tunica propria, is the submucous layer, or tela submucosa. 

 It is a vascular connective tissue by which the mucous membrane is at- 

 tached to underlying 'muscles or bones. All of the layers named are in- 

 volved in the tonsils which, how r ever, are essentially lymphoid accumula- 

 tions in the tunica propria. 



The epithelium of the palatine tonsils is a stratified epithelium of 

 many layers, with flattened cells on its smooth free surface, and columnar 





/ -- 



FIG. 190. VERTICAL SECTION OF A HUMAN PALATINE TONSIL. 



a, Stratified epithelium; b, basement membrane; c, tunica propria; d, trabeculae; e, diffuse lymphoid 

 tissue; f, nodules; h, capsule; i, mucous glands; k, striated muscle; 1, blood vessel; q, pits. (From 

 Radasch.) 



cells beneath. Its attached surface is invaded by connective tissue ele- 

 vations or papillae so that it appears wavy in sections (Fig. 190). The 

 stratified epithelium lines from ten to twenty almost macroscopic depres- 

 sions called tonsillar pits orfossulae (crypts). These are irregularly cylin- 

 drical and sometimes branched. Many lymphocytes penetrate between 

 the epithelial cells and escape from the free surface into the saliva, to be- 

 come 'salivary corpuscles.' In places the tonsillar epithelium is so full of 

 lymphocytes as to appear disintegrated. In the reticular tissue of the 

 tunica propria, especially around the pits, there are many lymph nodules, 

 some of which are well defined with germinative centers, but many others 

 are fused in indefinite masses. The lymphoid tissue forms the bulk of the 

 tonsil. 



