THE DIGESTIVE SYSTEM 



283 



These are continuous with the long narrow intermediate tubules, from 

 each of which are given off a number of short terminal tubules (Figs. 

 182 A, and 184). The two-layered epithelium of the main duct 

 becomes reduced in tlic smaller ducts to a single layer of columnar 

 cells. The salivary tubules are lined with high columnar epithelium, 

 the bases of the cells showing distinct longitudinal striations. In the 

 intermediate tubule the epithelium is flat, sometimes spindle-shaped. 

 The terminal tubules are lined with serous cells (page 226). The con- 

 nective tissue usually contains a considerable number of fat cells. 



The sublingual gland is a mixed gland in man, dog, cat, and 

 rabbit. The duct system is less complex than in the parotid. The 





^^ ~ Intercalated 



i- tubule 



i I 



I 



Fat cells Terminal tubule 



Fig. 184. — Section of Human Parotid Gland. X252. (Stohr.) The narrow lumina 



of the terminal tubules do not^show in this figure. 



main duct (Bartholini) sends off branches which are continuous with 

 tubules, showing a few secretory mucous cells. These open directly 

 into the terminal tubules which are convoluted and vary greatly in 

 diameter (Fig. 182, ^). The excretory duct is like that of the parotid 

 gland, lined with a two-layered columnar epithelium resting upon a 

 basement membrane. In the smaller ducts the epithelium is reduced 

 to a single layer of columnar cells. There are no intermediate 

 tubules . The terminal tubules are lined with both serous and mucous 

 cells (page 226). The crescents of Gianuzzi (page 227) are numerous 



