2 9 o HEAD AND NECK 



is formed by the basilar part of the occipital bone, and 

 also by a small part of the under surface of the basi-sphenoid, 

 both of which are covered with a dense periosteum and a 

 thick coating of mucous membrane. The posterior wall is 

 supported, posteriorly, by the anterior arch of the atlas and 

 the anterior surface of the epistropheus. In that part of the 

 roof which lies between the two pharyngeal recesses there 

 is a marked collection of lymphoid tissue, called the pharyngeal 

 tonsil. Over its surface the mucous membrane is thickened 

 and wrinkled, and in its lower part a small median pit, 

 termed the pharyngeal bursa, may sometimes be found ; the 

 bursa is just large enough to admit the point of a fine probe. 



The floor of the naso-pharynx is formed by the curved, 

 sloping upper surface of the soft palate. Between the posterior 

 border of the soft palate and the posterior wall of the pharynx 

 there is an interval, termed the naso-pharyngeal isthmus, through 

 which the naso-pharynx communicates with the oral pharynx. 



It is important to note that the posterior wall and roof of 

 the naso-pharynx can be explored by the finger introduced 

 through, the mouth and the naso-pharyngeal isthmus. 



When the naso-pharynx is illuminated, by light reflected 

 from a mirror introduced through the mouth, a view of the 

 four orifices which open into the nasal part of the pharynx 

 may be obtained. Owing to the mirror being placed 

 obliquely, and below the level of the hard palate, only the 

 posterior parts of the inferior conchse are visible through the 

 choanae, and the inferior meatuses of the nose are altogether 

 out of sight. The middle and superior meatuses of the nose 

 and the middle and superior conchse, however, can be brought 

 into view and their condition ascertained. The lateral walls 

 of the naso-pharynx and the orifices of the auditory tubes 

 also can be fully inspected. 



Pars Oralis. The oral pharynx lies posterior to the mouth 

 and tongue. The anterior wall of its lower part is formed 

 by the base or pharyngeal part of the tongue, which looks 

 more or less directly backwards. Above the tongue is the 

 isthmus of the fauces, or the opening into the mouth, limited 

 on each side by the glosso-palatine arch. The glosso-pala- 

 tine arches may be regarded, therefore, as the lateral boundary 

 lines between the mouth and the pharynx. On the side wall 

 of the oral pharynx the pharyngo-palatine arch forms a 

 prominent fold which gradually disappears as it passes back- 



