1132 DIGESTIVE SYSTEM 



limited anteriorly and posteriorly b}^ the anterior and posterior palatine arches, 

 and below by the root of the tongue. 



The palatine arches are folds of the mucosa formed at the sides of the free 

 posterior border of the soft palate, as already mentioned in connection with that 

 organ. The anterior arch (or pillar) [arcus glossopalatinus] extends from the 

 soft palate downward and forward to the lateral margin of the tongue, just behind 

 the papillae foliatse. It is a fold of mucosa due to the underlying glosso-palatine 

 muscle, and inconspicuous except when this muscle is in action, or when the 

 tongue is depressed. It forms the lateral boundary of the faucial isthmus. The 

 posterior arch [arcus pharyngopalatinus] is a more prominent fold which extends 

 from the soft palate in the region of the uvula downward and backward to join 

 the posterolateral aspect of the pharyngeal wall. It forms the lateral boundary of 

 the pharj-ngeal isthmus, and encloses the pharyngo-palatine muscle, whose action 

 will be explained later. 



The palatine tonsil [tonsilla palatina] (figs. 864, 889, 890, 891) is a flattened 

 ovoidal body, usually visible through the mouth cavity and faucial isthmus, and 

 located on each side of the oral pharynx. The tonsil is extremely variable in 

 size, but in the young adult averages about 20 mm. in height, 15 mm. in width 

 (antero-posteriorly) and 12 mm. in thickness. 



The lateral or attached surface of the tonsil is covered by a thin but firm 

 fibrous capsule, which is continuous with the pharyngeal aponeurosis, and in 

 contact with the middle constrictor muscle of the pharynx (fig. 864). Just out- 

 side the constrictor, the tonsil is in relation with the ascending pharyngeal and 

 ascending palatine arteries, but is separated by a considerable space from the 

 external and internal carotids. Rarely, however, the lingual or external maxil- 

 lary ma}^ extend up higher than usual, so as to be in close relation with the lower 

 aspect of the tonsil. Further lateralward, the palatine tonsil is in relation with 

 the internal pterygoid muscle, and on the surface corresponds to a point somewhat 

 above and in front of the angle of the mandible. The posterior border of the 

 tonsil is thicker than the anterior, and forms a somewhat flattened surface in con- 

 tact with the pharyngo-palatine muscle (fig. 891). 



The medial or free surface of the tonsil is covered with mucosa and presents a 

 variable number (12 to 30) small pits which are the openings into the tubular or 

 slit-like crypts [fossulse tonsillares]. These crypts are somewhat more numerous 

 in the upper part of the tonsil, and are sometimes branched or irregular in form. 

 Usually they end blindly in the substance of the tonsil, surrounded by lymphoid 

 tissue in characteristic nodular masses (fig. 889). The lymphocytes normally 

 migrate through the stratified squamous epithelium lining the crypts (occasion- 

 ally eroding passages of considerable size), and escape into the pharyngeal and 

 mouth cavities, where they form the so-called salivary corpuscles. Around the 

 periphery of the palatine tonsil, within the capsule, are many mucous glands (fig. 

 889), similar to those described in connection with the lingual and pharyngeal 

 tonsils. The ducts of the mucous glands sometimes enter the crypts, but usually 

 pass to the surface chiefly around the margins of the palatine tonsil. 



Tonsillar plicae and fossae. — Connected with the tonsil are certain important 

 folds and fossa'. The plica triangularis (fig. 891) is a fold of variable extent and 

 appearance, placed just behind the anterior arch, wider below and narrower 

 above. According to Fetterolf, it is a prolongation of the tonsillar capsule, cov- 

 ered with mucosa. It may be adherent to the anterior part of the medial surface 

 of the tonsil, or it may be free, in which case it covers a recess called the anterior 

 tonsillar fossa. Occasionally there is a similar plica and fossa at the posterior 

 border of the tonsil. A})ove the tonsil there is similarly a supratonsillar fossa 

 [fossa supratonsillaris], which is also inconstant and exceedingly variable in size 

 and shape. Killian found a supratonsillar fossa or canal in 41 of 105 cadavers. 



Tonsillar vessels. — Tho arlcrics to the tonsil include the anterior tonsillar (from the dorsalis 

 linnuii'j; the inferior tonsillar (from the external maxillary); the poslerior tonsillar (from the 

 asceiHlirifi; pharyngeal) and the nuperior tonsillar (from the descending i)alatine). These 

 pierce the capsule and sui)ply the jrland. The veins form a plexus around the capsule and empty 

 into the lingual vein and the jjliaryngeal plexus. The lymphatic relations of the palatine 

 tonsil are imj)ortaiit. Afferent vessels are received from acljacent areas of the mucosa in the 

 pharynx, mouth and lower part of the nasal cavity (v. Lenart). These are connected with an 

 extensive lymphatic plexus around the lymph foUich^s within the tonsil. Efferent lymphatic 

 vessels pass chiefly to the uf)per deep cervical lymphatic nodes. One of these, located just 

 behind the angle of the mandible, is so cl(jsely connected with the tonsil, and so constantly 



