MOUTH CAVITY. 171 



in a section they are cut at various angles. The main ducts, 

 which open into the mouth cavity, are covered by one or two 

 layers of cylindrical epithelium. In the connective tissue 

 which makes up their outer sheath, we often (submaxillary 

 duct) find smooth muscle fibres running longitudinally. The 

 main duct divides into many smaller branches (interlobular 

 ducts), which are lined with a single layer of cubical or cylin- 

 drical epithelium. Each of these smaller ducts passes over into 

 a salivary duct (intralobular duct), which is made up of cylin- 

 drical epithelium, whose cells are characterized by the fact that 



FIG. 126. 



\r Salivary duct 



Connective tissue 

 between lobules 



From a section through a dog's parotid gland. Several lobules are to be seen. -2-2. 



their basal ends are plainly striated. This striation is due to 

 small granules in the protoplasm, which are arranged in rows 

 (Figs. 127 and 130). While the interlobular ducts are always 

 present in the connective tissue between the lobules, the salivary 

 ducts or intralobular ducts are in the lobule itself. The intra- 

 lobular divides in the lobule, and each division passes over into 

 a so-called intercalary part, or intermediate duct, which is a 

 tube lined with low cubical epithelium (Figs. 129 and 130; Fig. 

 127). Many authors have ascribed to the intralobular ducts 

 secretorv functions, while the interlobular ducts conduct the 



