1232 



THE ORGANS OF DIGESTION 



of the second branchial cleft. The posterior wall of the nasopharynx is directed 

 upward and forward, and it meets the superior wall at an angle constituting the 

 vault of the pharynx (fornix pharyngis). On the posterior wall, above the level 

 of the orifices of the Eustachian tubes, is a prominence, best marked in childhood, 

 produced by a mass of lymphoid tissue which is known as the pharyngeal tonsil 

 (tonsiUa pharyngea) (Fig. 948). In the pharyngeal vault, in the middle line, 

 an irregular flask-shaped depression of the mucous membrane is sometimes seen 

 extending up as far as the basilar process of the occipital bone. It is known as 

 the pharyngeal bursa, a possible vestige of the pharyngeal tonsil. The floor of the 

 nasopharynx is formed by the upper surface of the sloping soft palate; in front 

 the floor is continuous with that of the nasal cavities, while behind it ends at the 

 free margin of the soft palate, which bounds the isthmus of the pharynx (isthmus 

 pharyngonasalis). 



The Oral Part (pars oralis pharyngis) of the pharynx reaches from the under 

 surface of the soft palate to about the level of the hyoid bone. It opens ante- 

 riorly, through the isthmus faucium, into the mouth, while in its lateral wall, 

 between the two pillars of the fauces, is the tonsil. 



ORIFICE OF 



EUSTACHIAN 



TUBE 



PHARYNGEAL 



BURSA 



SALPINGO- 



NASAL FOLD 



EUSTACHIAN 



CUSHION 



SALPINGO- 

 PALATINE FOLD 



SALPINGO-PHARYN- 

 GEAL FOLD 



FIG. 948. Pharyngeal tonsil in an adult 

 (Escat.) 



FIG. 949. The posterior lateral cavity of the naso- 

 pharynx. (Escat.) 



The Tonsils (tonsilla palatina) (Figs. 914 and 950) are two prominent bodies 

 situated one on each side of the fauces, between the anterior and posterior pillars 

 of the soft palate. They are of a rounded form, and vary considerably in size 

 in different individuals. A recess, the supratonsillar fossa (fossa sujtratonsillaris), 

 may be seen, directed upward and backward above the tonsil, the recess being 

 the remains of the lower part of the second visceral cleft. It is covered by a fold 

 of mucous membrane termed the plica triangularis. Externally the tonsil is covered 

 with a fibrous capsule which joins the aponeurosis of the pharynx. The outer 

 surface of the capsule is in relation with the inner surface of the Superior constrictor 

 muscle of the pharynx, to the outer side of which is the Internal pterygoid muscle, 

 the ascending palatine artery, the Superior constrictor muscle of the pharynx, and 

 the tonsillar artery. The internal carotid artery lies behind and to the outer side 

 of the tonsil, and nearly an inch (20 to 25 mm.) distant from it. It corresponds 

 in position to the angle of the mandible. The surface of the tonsil which looks 

 toward the pharynx presents from twelve to fifteen orifices, each leading into 

 small recesses or crypts (fossulae tonsillares). From the crypts numerous follicles 

 branch out into the substance of the tonsil by means of very irregular channels. 



Structure. The tonsil is covered externally by a capsule of white fibrous tissue that separates 

 it from the surrounding organs and tissues. This capsule sends in trabecula? that divide the 



