Chap, xxii.] 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 

 fibrillae (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, hence 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 and 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. That 

 part of the duct which is in immediate connection with 

 the alveoli is the intermediary part, this being inter- 

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

 tube with fibrillated epithelium. The intermediary 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 intermediary 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 intermediary 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 intermediary part. In 

 some salivary glands, especially in the mucous, this 



