THE THYMUS 



157 



The Lingual Tonstt. A collection of lymphatic follicles is also 

 found at the base of the tongue in the median line, between the 

 circumvallate papillae and the epiglottis. This, because of its 



FIG. 153. THE LINGUAL TONSIL OF MAN. 

 a, a crypt ; 6, von Ebner's glands. Hematein and eosin. x 45. 



similarity in appearance and in structure to the faucial tonsil, is 

 called the lingual tonsil. 



In the lingual tonsil, however, the follicles are grouped about 

 a single wide-mouthed crypt, the foramen ccecum lingui. This 

 crypt is frequently branched, and into it the many mucous glands 

 of the neighboring lingual mucosa pour their secretion. 



The Pharyngeal Tonsil. The posterior wall of the naso-pharynx 

 is supplied with a similar accumulation of lymphatic follicles, the 

 pharyngeal tonsil. It lies in the median line and extends down- 

 ward from between the orifices of the Eustachian tubes for a dis- 

 tance of three centimetres (Klein). It contains a considerable 

 number of lymphatic follicles and several small crypts. 



The pharyngeal tonsil is prone to hypertrophy in youth, in 

 which case it forms the adenoid growths which are so common in 

 strumous children. 



THE THYMUS. The thymus is an organ of fetal and infantile 

 life, attaining its maximum development during the second year 



