Chap, xxii.] THE SALIVARY GLANDS. 183 



of rabbit and guinea-pig, the salivary cells form a 

 single layer of shorter or longer columnar or pyra- 

 midal albuminous cells, composed of a densely reticu- 

 lated protoplasm, and containing a spherical nucleus in 

 the outer part of the cell. (2) In the mucous glands, 

 such as the sub-lingual of the guinea-pig, or the 

 admaxillary of the same animal, the cells lining the 

 alveoli form a single layer of goblet-shaped mucous 

 cells, such as have been described in par. 25. Each 

 cell consists of an inner principal part, composed of a 

 transparent rnucoid substance (contained in a wide- 

 meshed reticulum of the protoplasm), and an outer 

 small, more opaque part, containing a compressed and 

 flattened nucleus. This part is drawn out in a fine 

 extremity, which, being curved in a direction parallel 

 to the surface of the alveolus, is imbricated on its 

 neighbours. 



245. In the case of the sub-maxillary and orbital 

 glands of the dog, the sub-lingual of rabbit, there exist, 

 in addition to, and outside of the mucous cells lining 

 the alveoli, but within the meinbrana propria, from 

 place to place crescentic masses, being the demilunes 

 of Heidenhain, or the crescents of Gianuzzi (see Fig. 

 107). Each is composed of several polyhedral granu- 

 lar-looking cells, each with a spherical nucleus ; the 

 cells at the margin of the crescent are of course 

 thinner than those forming the middle. Heiden- 

 hain and his pupils, Lavdovski and others, have 

 shown that, during prolonged exhausting stimula- 

 tion of the sub-maxillary and orbital of the dog, 

 all the lining cylindrical mucous cells become re- 

 placed by small polyhedral cells, similar to those 

 constituting the crescents, while at the same time 

 the alveoli become smaller (Fig. 108). These ob- 

 servers maintain that this change is due to a total 

 destruction of the mucous cells, and a replacement 

 of them by new ones, derived by multiplication 



