1586 



HUMAN ANATOMY. 



The parotid gland consists entirely of serous alveoli, although mucus-pro- 

 ducing acini may occur in the accessory lobules situated along the duct of Stenson. 

 The primary lobules are made up of alveoli, from .015 to .020 mm. in diameter, lined 

 with epithelial cells, which are somewhat pyramidal in form, since they are broader 

 next the basement membrane and narrower towards the cleft-like lumen. The rest- 

 ing cells, fresh and examined without the addition of reagents, appear filled with 

 numerous minute, glistening granules which lie embedded within a less strongly 

 refracting substance. The granules, however, are readily affected by reagents, often 

 undergoing partial or complete solution; hence the reticulated appearance of the pro- 

 toplasm frequently observed in glandular epithelium after fixation. The nuclei of 

 the serous cells are usually of spherical form and contain distinct nucleoli and delicate 



Fig. 1346. 



Interlobular duct 



Interlobular septum 



Section of small lobule of parotid gland. X 80. 



chromatin net-works. The system of excretory canals begins at the alveoli as the 

 intermediate tubules, which in the parotid are relatively long, about .010 mm. in 

 diameter, and lined with low, flattened cells, directly continuous with the taller alveolar 

 epithelium, on the one hand, and with that of the intralobular ducts on the other. 

 The latter, or salivary tubules of Pf^iiger, of larger diameter (about .035 mm.) than 

 that of the immediately preceding or succeeding segments of the canal, are clothed 

 with a single layer of columnar cells, some .014 mm. in height, which present a 

 peculiar differentiation into an inner and an outer zone. The former, next the 

 lumen of the tube and containing the nucleus, appears finely granular or almost 

 homogeneous, while the outer or basal zone exhibits a longitudinal striation composed 

 of rows of minute granules. After treatment with certain reagents, the striated zone 



