Chap, xxn.] THE SALIVARY GLANDS. 181 



propria, with a single layer of columnar epithelial cells. 

 Each of these has a spherical nucleus in about the 

 middle; the outer half of the cell substance shows 

 very marked longitudinal striation, due to more or 

 less coarse fibrillse (see Fig. 106). The inner half, 

 i.e., the one bordering the lumen of the duct, is only 

 very faintly striated. The outline of these salivary 

 tubes is never smooth, but irregular, i.e. y the diameter 

 of the tube varies from place to place. 



Not in all salivary glands do the epithelial cells 

 of the intralobular ducts show this coarse fibrillation 

 in the outer part of their substance; e.g., it is not 

 present in the sub-lingual gland of the dog or the 

 guinea-pig. 



242. The ends of the branches of the salivary 

 tubes are connected with the secreting parts of the 

 lobule, i.e., the acini or alveoli These always very 

 conspicuously differ in structure from the salivary 

 tubes, and, as a rule, are larger in diameter. The last 

 part of the duct which is in immediate connection with 

 the alveoli is the intermediate part, this being inter- 

 posed, as it were, between the alveoli and the salivary 

 tube with fibrillated epithelium. The intermediate part 

 is much narrower than the salivary tube, and is lined 

 with a single layer of very flattened epithelial cells, 

 each with a single oval nucleus; the boundary is 

 formed by the membrana propria, continued from the 

 salivary tube. The lumen of the intermediate part is 

 much smaller than that of the salivary tube, and is 

 generally lined with a fine hyaline membrane, with 

 here and there an oblong nucleus in it. 



At the point of transition of the salivary tube 

 into the intermediate part there is generally a sudden 

 diminution in size of the former, and the columnar 

 cells of the salivary tube are replaced by polyhedral 

 cells ; this is the neck of the intermediate part. In 

 some salivary glands, especially in tho mucous, this 



