, MOUTH 237 



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 54) 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 refract- 

 ive granules. In fixed preparations they may appear dark and granular 

 (empty of secretion) or enlarged and somewhat clearer (full of secretion), 

 as shown in Fig. 44, p. 54. The round nucleus is generally in the basal 

 half of the cell, not far from its center (Fig. 227). Mucous cells when 



Man. Rabbit. Man. 



d 



Mucous glands. Serous glands. 



TUBULES, FROM LINGUAL GLANDS, ILLUSTRATING THE DIFFJ 



Mucous AND SEROUS GLAND CELLS. 

 b, Empty mucous cells; c, mucous cells full of secretion; d, lumen of the tubule. X 240. 



FIG. 227. SECTIONS OF TUBULES, FROM LINGUAL GLANDS, ILLUSTRATING THE DIFFERENCES BETWEEN 



Mucous AND SEROUS GLAND CELLS. 



fresh are much less refractive than serous cells. In fixed preparations 

 they are typically clear, since the large area occupied by mucous secretion 

 stains faintly. Fully elaborated mucus, however, may be colored intensely 

 with certain aniline dyes, such as mucicarmine and Delafield's haematoxy- 

 lin. In certain types of mucous cells the pale secretion area is large in 

 all stages of activity. When full of mucus, the nucleus is flattened against 

 the base of the cell, and when empty, the nucleus becomes more oval with- 

 out essentially changing its position (Fig. 227). This differs from the type 

 of mucous cell found in the gastric epithelium, in which the secretion area 

 varies 'considerably with the elaboration and discharge of secretion (Fig. 



45, P- 55)- 



Glands may consist entirely of serous or of mucous cells, but frequently 



they include cells of both sorts and are called mixed glands. The mixed 

 glands contain some purely serous tubules or alveoli; the rest consist of 

 both mucous and serous cells, so arranged that the latter appear more or 

 less crowded away from the lumen. Often they form a layer outside of 

 the mucous cells, partly encircling the tubule or alveolus and constituting 

 a crescent (demilune), as shown in Fig. 237. The serous cells of the cres- 



