78 SPECIAL HISTOLOGY. 



OF THE ORGANS OF DEGLUTITION. 



1. THE PHARYNX. 



§144. 



The alimentary canal assumes a greater independence in 

 the pharynx, acquiring a special investment of transversely 

 striated muscles, the constrictores and levatores, which, however, 

 do not entirely surround it and arise for the most part from 

 bones. The thickness of the walls of the pharynx is about 2'" 

 on an average, depending principally upon this muscular 

 layer, external to which there is a tense fibrous membrane, 

 composed of connective tissue and elastic fibres, while internally 

 it is separated by a layer of submucous connective tissue from 

 the mucous membrane. The latter is paler than that of the 

 oral cavity and its structure in the upper half of the pharynx 

 differs considerably from that in the lower half. In the latter 

 locality, that is, below the pharyngo-palatine arches, or in the 

 region through which the food passes, it possesses a tesselated 

 epithelium similar in structure and thickness to that of the 

 oral cavity j above them, on the other hand, that is, on the 

 posterior surface of the soft palate from its free edge, upon 

 the upper surface of the uvula, in the region of the choancR 

 and Eustachian tubes, and upon the vault of the pharynx, 

 there is a ciliated epithelium like that in the nasal cavity 

 and larynx, to the description of which, below, the reader 

 may be referred. In this upper or respiratory section 

 the mucous membrane is also redder, thicker, and more glan- 

 dular than in the lower division, otherwise, however, its struc- 

 ture is pretty much the same, with the exception that it pre- 

 sents no papillae, which however, in some parts of the lower 

 division are very little developed and rare, and would even 

 appear to be entirely wanting. Compared with that of the oral 

 cavity I find the mucous membrane of the pharynx to possess 

 much more and much stronger elastic tissue, which, in the 

 deeper layers, forms connected, very dense, elastic membranes. 



The pharynx contains two sorts of glands ; 1. racemose mu- 

 cous glands (vide supra, § 134), and, 2. follicular glands. The 



