1142 



THE DIGESTIVE SYSTEM. 



neighbouring cavities (Fig. 901). These are the two choanae (O.T. posterior nares) 

 on the anterior wall of the pars nasalis, and the two tubse auditivae (O.T. Eusta- 

 chian tubes) on its side walls ; the isthmus of the fauces, leading into the mouth 

 from the oral part ; the orifice of the larynx on the anterior wall of the laryngeal 

 part of the cavity ; and finally, the opening of the oesophagus at its inferior end. 



Pars Nasalis(O.T. Naso-Pharynx) (Figs. 901 and 902). Although morphologic- 

 ally and developmentally this is a portion of the true pharynx, it is functionally an 

 annexe to the respiratory portion of the nasal cavities, and both anatomically and 



Posterior end of 

 middle concha' 



Pharyngeal tonsil 



Maxillary sinus 



Posterior end of 

 inferior concha 



Glands in hard 

 palate 



Third molar 



Uvula 



-Orbit 



Posteiior edge of 

 nasal septum 



Torus tubarius 



Pharyngeal orifice of 

 'auditory tube 



Glosso-palatine 

 'arch 



Palatine tonsil 

 Buccinator (cut) 



Pharyngo-palatine 

 arch 



Pharyngo-nasal 



isthmus 



Tongue 



FIG. 902. THE NASAL PART OF THE PHARYNX FROM THE FRONT. 



A frontal section was made through the upper part of the head ; this passed immediately in front o 

 the posterior edge of the nasal septum, and extended into the mouth below. Through the choanae, 

 the nasal part of the pharynx is seen. The prominence of the posterior margin of the ostium pharyn- 

 geum of the auditory tube, and the lymph nodules constituting the pharyngeal tonsil, should be noted. 

 The palatine arches and tonsils, and an unusually wide pharyngo-nasal isthmus, are also seen. 



functionally it is distinctly marked off from the digestive tube. It differs from 

 the rest of the pharynx in that its cavity remains, under all conditions, a distinct 

 open chamber incapable of obliteration, owing to the fact that all its walls, with 

 the single exception of the floor, are practically immovable. 



The cavity of the pars nasalis is irregular in shape, and is enclosed by sw 

 walls namely, anterior and posterior, right and left, a floor and a roof or vault. 



These walls all merge into one another, and the lines of separation between them an 

 arbitrary. Through the anterior wall, which slopes upwards and backwards, open th< 

 choanae (O.T. posterior nares), separated from each other by the nasal septum, 

 margins of the choanae form the line of separation between the pars nasalis and the cavity 

 of the nose. This separation is occasionally marked by a furrow or fold 011 the sid< 

 wall, called the naso-pharyngeal furrow. 



