DIGESTIVE SYSTEM. 



137 



and the tongue is attached to the movable floor, 

 while posteriorly it opens into the pharynx through 

 the isthmus or fauces. This cavity is lined by a con- 

 tinuous mucous membrane, consisting of stratified 

 mucous epithelium placed on a tunica propria. In 



Sinus pracervicalis. 



Fig. 99. Human embryo of about twenty-eight days (His): I-V, 

 brain-vesicles; f 1 , / 2 , / 3 , / 4 , cephalic, cervical, dorsal, and lumbar flexures; 

 ot, otic vesicle; ol, olfactory pit; mx, maxillary process; h\ W y heart; 

 /, I 1 , limbs; a Is, allantoic stalk; ch, villous chorion. 



the submucosa is found connective-tissue elements 

 in which the elastic fibers predominate; also con- 

 nective-tissue cells, mucous and serous glands, 

 nerves, and nerve endings, blood- and lymph- vessels. 



