184 THE ORGANS 



only a few lymphoid cells scattered among the epithelium, to an almost 

 complete replacement of epithelial by lymphoid tissue. In this way 

 the latter reaches the surface and lymphoid cells are discharged upon 

 the surface of the tonsil and into the crypts. These cells probably 

 form the bulk of the so-called salivary corpuscles. In the connective 

 tissue adjacent to the tonsil are numerous mucous glands, the ducts 

 of which empty into the tonsillar crypts. 



The Lingual Tonsils— Folliculi Linguales. — These are small 

 lymphatic organs situated on the dorsum and sides of the back part 

 of the tongue between the circumvallate papillae and the epiglottis. 

 They are similar in structure to the true tonsils. Each Ungual 

 tonsil has usually one rather wide-mouthed deep crypt (the forafuen 

 ccBcum lingiics) which may be branched and which is Hned with a 

 continuation of the surface stratified squamous epithelium. Arranged 

 around the crypt are the lymph nodules, each usually having a 

 distinct germinal center and more or less sharply separated from the 

 surrounding tissue by a fibrous capsule. In most crypts there is 

 marked lymphoid infiltration of the epithelium with free "salivary 

 corpuscles." Into these crypts frequently open the ducts of some 

 of the mucous glands of the tongue. 



The Pharyngeal Tonsils.- — These are lymphatic structures which 

 lie in the naso-pharynx. They resemble the lingual tonsils, except 

 that they are, as a rule, not so sharply circumscribed. Hypertrophy 

 of the pharyngeal tonsils, with consequent obstruction of the nasal 

 openings, is common especially in children, constituting what are 

 known as adenoids. 



The blood-vessels have a distribution similar to those of the 

 lymph nodes, but enter the organ along its entire attached side and 

 not at a definite hilum. 



Of the lymphatics of the tonsil little is known. 



The nerves wliich are branches of the glosso-pharyngeal and of 



the spheno-palatine ganglion also enter the organ along its attached 



side. 



The palatine tonsils make their first appearance during the third month of 

 intra-uterine life as hollow evaginations of entoderm which grow down into 

 the underlying mesenchyme, in the region of the second inner branchial 

 groove. The earliest of the tonsillar lymphoid cells are apparently white 

 blood cells which have migrated from the vessels of the stroma of the mucosa 

 and have infiltrated the surrounding connective tissue. Further development 

 of the tonsil is by proliferation of these cells. The crypts are at first solid 

 ingrowths of surface epithelium. These later become hollowed out. 



