~ ~/ Axial lumen. 



238 HISTOLOGY 



cent are connected with the lumen by means of secretory capillaries (p. 57) 

 which pass out to them between the mucous cells and branch around the 

 serous cells, ending blindly (Fig. 228). Sometimes the cells of the crescent 

 are directly in contact with the lumen. Since the serous crescents are 

 always associated intimately and somewhat irregularly with mucous cells, 



they were naturally interpreted as a func- 

 tional phase of the latter. It is probably 

 true that some crescents represent empty 

 mucous cells which have been crowded 

 from the lumen by those full of secretion. 

 No secretory capillaries lead to such 

 mucous crescents, which moreover are 

 not abundant. Another sort of crescen- 

 tic figure is made by the basal protoplasm 



Crescent. * 



FIG. 228. FROM A SECTION OF THE SUBMAX- in mucous cells otherwise full of secre- 



ILLARY GLAND OF A DOG. X 320. 



tion. Finally, in oblique sections, stel- 

 late cells associated with the basement membrane may resemble true 

 crescents. 



The oral glands include serous glands, mucous glands, and mixed glands 

 to be described in turn. 



Intercellular 

 secretory 

 capillary. 



Serous Glands. 



The serous oral glands are the parotid glands and the serous glands 

 of the tongue (v. Ebner's glands). The latter are branched tubular 

 glands limited to the vicinity of the vallate and 

 foliate papillae. Generally they open into the 

 grooves which bound these papillae. Their ducts 

 are lined with simple or with stratified epithelium, 

 which is occasionally ciliated. Their small tubules 

 consist of a delicate membrana propria or basement 

 membrane, which surrounds the low columnar or 

 conical serous cells. In this simple epithelium, 

 cell walls are lacking. With special stains and 

 high magnification, a dark granular zone toward 

 the lumen has been distinguished from the clear 

 basal portion of the cell which contains the nu- 

 cleus (Fig 229). The lumen of the tubules is 

 very narrow and receives the still narrower intercellular secretory capil- 

 laries (Fig. 230). 



The parotid glands are the largest oral glands. Each is situated in 

 front of the ear and is folded around the ramus of the mandible; its duct, 

 the parotid duct (Stenson's), empties into the mouth opposite the second 



FIG. 229. TUBULE OF A SER- 

 OUS GLAND FROM THE HU- 

 MAN TONGUE. X 750. 



Secretory granules toward the 

 lumen are finer than those 

 further out. The light in- 

 tercellular lines represent the 

 secretory capillaries. 



