GLANDS OF THE ORAL CAVITY. 185 



of the pharynx. It increases in thickness upward, at the expense of the 

 submucosa, so that it forms a thick layer in the back of the pharynx in con- 

 tact with the muscles, among the fibers of which it sends prolongations. 

 This elastic layer, as the fascia pharyngobasilaris, is attached to the base of 

 the skull. 



In most of the oral region there is no sharp line of separation between 

 the propria and the submucosa. The latter may be a loose layer contain- 

 ing fat, and allowing considerable movement of the mucosa, or, as in the 

 gums and hard palate, it may be a dense layer binding the membrane 

 closely to the periosteum. In the submucosa are the branches of various 



Epithelium. ' 



Tunica propria. 



Submucosa. 



FIG. 207. VERTICAL SECTION THROUGH THE Mucous MEMBRANE OP THE LIP OF AN ADULT MAN. X 30. 

 i, Papilla; 2, excretory duct; the lumen is cut at only one point; 3, accessory gland; 4, a branch of the 



excretory duct in transverse section; 5, gland bodies grouped into lobules by connective tissue; 6, a 



gland tubule in transverse section. 



glands. On the inner border of the lips and the inner surface of the cheek 

 there are sebaceous glands without hairs, which first develop during puberty. 

 This type is described with the skin. The other oral glands are considered 

 in the following section. 



GLANDS OF THE ORAL CAVITY. 



In the general account of glands (page 32) it has been stated that 

 serous gland cells which produce a watery albuminoid secretion should be 

 distinguished from the mucous gland cells which elaborate thick mucus. 

 When examined fresh, serous cells are seen to contain many highly refrac- 



