CH. XXVII.] THE ALIMENTARY CANAL. 439 



THE MOUTH. 



This cavity is lined by a mucous membrane consisting of a 

 corium of fibrous tissue with numerous patches of lymphoid 

 tissue in it, especially in the posterior regions ; and an epithelium 

 of the stratified variety closely resembling the epidermis. The 

 surface layers, like those of the epidermis, are made of horny 

 scales. Opening into the mouth are a large number of little 

 mucous glands, and the salivary glands pour their secretion into 

 the mouth also. The teeth (p. 70) have been previously studied. 

 The tongue will be considered later in connection with taste. 



THE PHARYNX. 



That portion of the alimentary canal which intervenes between 

 the mouth and the oesophagxis is termed the Pharynx. It 

 is constructed of a series of three mus- 

 cles with striated fibres (constrictors), 

 which are covered by a thin fascia ex- 

 ternally, and are lined internally by a 

 strong fascia (pharyngeal aponeurosis), 

 on the inner aspect of which is areolar 

 {submucous) tissue and mucous mem- 

 brane, continuous with that of the mouth, 

 and, as regards the part concerned in 

 swallowing, is identical with it in general 

 structure. The epithelium of this part Fig. 370. Lingiwi follicle or 



. , v \ , , , crypt, o, involution of 



Of the pharynx, like that Of the mouth, mucous membrane with 



is stratified. The upper portion of the 



pharynx into which the nares open is phoid nodules. (Prey.) 



lined with ciliated epithelium. 



The pharynx is well supplied with mucous glands. 



Between the anterior and posterior arches of the soft palate are 

 situated the Tonsils, one on each side. A tonsil consists of an 

 elevation of the mucous membrane presenting 1 2 to 1 5 orifices, 

 which lead into crypts or recesses, in the walls of which are 

 placed nodules of lymphoid tissue (fig. 371). These nodules are 

 enveloped in a less dense adenoid tissue which reaches the mucous 

 surface. The surface is covered with stratified epithelium, and 

 the corium may present rudimentary papillse formed of adenoid 

 tissue. The tonsil is bounded beneath by a fibrous capsule 

 (fig. 371,4). Into the crypts open the ducts of numerous mucous 

 glands. 



