MOUTH CAVITY. lt>i) 



(Fig. 124). The lymphocytes which escape at these places 

 form the salivary corpuscles of the saliva. The adenoid tissue 

 under the epithelium is divided into follicles which resemble 

 those of the lymph glands, possessing a germinal centre and a 

 dense periphery. 



The ducts of the mucous glands of the root of the tongue 

 often open into the crypts. 



The palatine tonsils have a structure similar to that of the 

 lingual tonsils, with the exception of being much larger and 

 possessing ten to twenty follicles and a number of crypts 

 (Plate XIL, Fig. 125). The follicles are situated at about the 

 same level as the tunica propria and possess usually very dis- 

 tinct germinal centres. The epithelium covering them is in 

 many places pierced partly or completely by an encroachment 

 of the adenoid tissue. The crypts always contain a number of 

 lymphocytes and may be branched. 



The tonsils can easily be seen at the pillars of the fauces, 

 and when inflamed may become so large that they almost or 

 quite meet in the median line. 



The pharyngeal tonsils lie at the upper part of the pharynx, 

 mainly in the naso-pharynx. Their structure is essentially the 

 same as that of the palatine tonsils. The crypts are clothed 

 often with ciliated epithelium, and are five or six in number. 

 Into these open the mixed glands, which form a distinct layer 

 under the follicles. There is here also a migration of lympho- 

 cytes through the epithelial covering of the organ. It is these 

 tonsils which on hypertrophy form the so-called adenoids which 

 often are found in children. 



Development of Tonsils. 



The development of lingual tonsils begins, according to 

 Stohr, in the eighth month of foetal life. Leucocytes wander 

 out from the veins of the tunica propria and infiltrate the loose 

 connective tissue around the ducts of the mucous glands. The 

 further growth of the adenoid tissue thus formed takes place 

 by the continued migration of leucocytes and by mitotic divi- 

 sion of these. The wandering of leucocytes from the lingual 



