1138 



SPLANCHNOLOGY 



does not completely fill the interval between the two arches, so that a small depres- 

 sion, the supratonsillar fossa, exists at the upper part of the interval. Further, 

 the tonsil extends for a variable distance under cover of the glossopalatine arch, 

 and is here covered by a reduplication of mucous membrane; the upper part of this 

 fold reaches across the supratonsillar fossa, between the two arches, as a thin 

 fold sometimes termed the plica semilunaris ; the remainder of the fold is called the 

 plica triangularis. Between the plica triangularis and the surface of the tonsil is 

 a space known as the tonsillar sinus ; in many cases, however, this sinus is obliterated 

 by its walls becoming adherent. From this description it will be apparent that a 

 portion of the tonsil is below the level of the surrounding mucous membrane, i. e., is 

 imbedded, while the remainder projects as the visible tonsil. In the child the 

 tonsils are relatively (and frequently absolutely) larger than in the adult, and about 

 one-third of the tonsil is imbedded. After puberty the imbedded portion diminishes 

 considerably in size and the tonsil assumes a disk-like form, flattened from side 

 to side; the shape and size of the tonsil, however, vary considerably in different 

 individuals. 





FIG. 1027. Section through one of the crypts of the tonsil. (Stohr.) Magnified, e. Stratified epithelium of general 

 surface, continued into crypt. /, /. Nodules of lymphoid tissue opposite each nodule numbers of lymph cells are 

 passing into or through the epithelium, s, s. Cells which have thus escaped to mix with the saliva as salivary corpuscles. 



The medial surface of the tonsil is free except anteriorly, where it is covered by 

 the plica triangularis; it presents from twelve to fifteen orifices leading into small 

 crypts or recesses from which numerous follicles branch out into the tonsillar 

 substance. 



The lateral or deep surface is adherent to a fibrous capsule which is continued 

 into the plica triangularis. It is separated from the inner surface of the Constrictor 

 pharyngis superior usually by some loose connective tissue; this muscle intervenes 

 between the tonsil and the external maxillary artery with its tonsillar and ascend- 

 ing palatine branches. The internal carotid artery lies behind and lateral to the 

 tonsil at a distance of 20 to 25 mm. from it. 



The tonsils form part of a circular band of adenoid tissue which guards the 

 opening into the digestive and respiratory tubes. The anterior part of the ring 

 is formed by the submucous adenoid collections (lingual tonsil) on the posterior 

 part of the tongue; the lateral portions consist of the palatine tonsils and the ade- 



