TIIF. DTCF.STIVE SYSTEM 227 



appears darker and less transparent. (}~Mucous tubules are larger 

 and more irregular in shape than serous tubules, and when stained 

 with haematoxyhn-eosin either remain almost wholly unstained or 

 take a pale blue hoematoxylin stain (Fig. 185, p. 284). Many 

 mucous tubules have, in addition to the mucous cells ,a pecuUar, often 

 crescentic-shaped group of cells on one side of the tubule, between 

 the mucous cells and the basement membrane. These cells are 

 granular and stain very much Hke serous cells with ha^matoxylin- 

 eosin, thus resembling the latter in appearance. On account of the 

 shape of the groups, they are known as the crescents of Gianuzzi or 

 demilunes of Ileidenhain (Fig. 185, p. 284). The cells of the crescents 

 are connected with the lumen by means of secretory canals, which 

 pass between the mucous cells and end in branches within the proto- 

 plasm of the crescent cells. It is quite possible that some of the 

 crescents are not serous cells but mucous cells in the non-active 

 condition which have been pushed away from the lumen by the more 

 active cells. Such cell groups are not connected with the lumen of 

 the gland by intercellular secretory canals. 



Peculiar irregular branching cells have been described, extending 

 from the basement membrane in between the mucous cells. They 

 are known as "basket" cells and are supposed to be supportive in 

 character. 



The cells of both mucous and serous tubules rest upon a membrana 

 propria, outside of which, separating the tubules, is a cellular connect- 

 ive-tissue stroma. 



Of the small glands of the mouth, a group near the root of the 

 tongue are of the mucous variety, some "lingual" glands in the region 

 of the circumvallate papillae are serous, while the remainder are of 

 the mixed type. 



Blood-vessels. — The larger vessels run mainly in the submucosa. 

 The arteries of the submucosa give off one group of branches to the 

 tunica propria, where they break up into a dense subepithelial capil- 

 lary network, sending capillary loops into the papillae. A second 

 group of arterial branches passes to the submucosa, and gives 

 rise to capillary networks among the tubules of the mucous glands. 

 From the capillaries veins arise which accompany the arteries. 



Lymphatics. — The larger lymph vessels lie in the submucosa. 

 These send smaller branches into the tunica propria, where they open 

 into small lymph capillaries and spaces. 



Nerves. — Medullated nerve fibres form plexuses in the submucosa 



