PHARYNX 291 



wards and downwards. Within the fold is the pharyngo- 

 palatine muscle, which is of importance because the posterior 

 palatine arches form the boundaries of the naso-pharyngeal 

 isthmus, on each side, and by the contraction of the pharyngo- 

 palatine muscles the two pharyngo- palatine arches can be 

 approximated until the opening of the isthmus is obliterated ; 

 the passage of food and fluids from the oral pharynx into 

 the naso-pharynx is thus prevented. 



The glosso-palatine arch and the pharyngo-palatine arch 

 form, on each side-wall of the oral pharynx, the anterior and 

 posterior limits of a triangular interval in which is lodged the 

 palatine tonsil. The upper part of the interval, above the 

 level of the tonsil, forms a small depression termed the supra- 

 tonsillar fossa. 



In the child, and not uncommonly in the adult, a triangular 

 fold of mucous membrane, called the plica triangularis, ex- 

 tends backwards from the lower part of the glosso-palatine 

 arch and the base of the tongue across the surface of the 

 palatine tonsil. The upper border of the fold may be free 

 or it may become attached to a greater or less extent to the 

 surface of the tonsil. 



Pars Laryngea. The laryngeal portion of the pharyngeal 

 cavity diminishes rapidly in width to the level at which it be- 

 comes continuous with the oesophagus. In its anterior wall, from 

 above downwards, may be seen: (i) the epiglottis; (2) the 

 superior aperture of the larynx, with a recessus piriformis on 

 each side ; and (3) the posterior surfaces of the arytsenoid 

 and cricoid cartilages, covered with muscles and mucous 

 membrane. 



Aditus Laryngis. The superior aperture of the larynx, 

 situated below the pharyngeal part of the tongue, is a 

 large, obliquely placed opening which slopes rapidly from 

 above downwards and backwards. It is somewhat triangular 

 in outline. The basal part of the opening, placed above and 

 anteriorly, is formed by the free border of the epiglottis. 

 Posteriorly, the opening rapidly narrows, and it ends in the 

 interval between the two arytaenoid cartilages. The sides of 

 the aperture are formed by two sharp and prominent folds 

 of mucous membrane, termed the ary-epiglottic folds, which 

 connect the right and left margins of the epiglottis with the 

 corresponding arytsenoid cartilages. Two small nodules of 

 cartilage, in the posterior part of each ary-epiglottic fold, 



