THE DIGESTIVE SYSTEM 43 



the mouth and pharynx is covered by a 

 stratified epithehum, the surface layers of 

 which are scaly and horny. At the margins 

 of the openings into the nasal chambers and 

 the larynx the epithelium is continuous with 

 the columnar and ciliated cells covering the 

 mucous membrane of these cavities. The oral 

 and pharyngeal mucous membrane itself con- 

 tains no glands, but in the underlying sub- 

 mucous tissue Heidrich has demonstrated the 

 presence of the following : — (1) Maxillary glands 

 in the roof of the mouth ; (2) palatine glands 

 on each side of the common opening from the 

 nasal chambers ; (3) spheno-pterygoid glands in 

 the roof of the pharynx on each side of the 

 common opening of the auditive tubes ; (4) 

 anterior submaxillary glands in the angle formed 

 by the union of the two halves of the mandible ; 

 (5) posterior submaxillary glands, arranged in 

 three groups ; (6) lingual glands in the tongue ; 

 (7) crico- arytenoid glands about the opening 

 into the larynx ; and (8) a gland at the angle 

 of the mouth. 



According to Heidrich, all these glands 

 produce a mucous secretion ; i.e. none of them 

 are structurally or physiologically equivalent 

 to the parotid gland of mammals. 



