208 



THE SALIVARY GLANDS, 



each lobe in turn of a number of lobules, which, again, are composed of acini. All these are held 

 together by a framework of connective-tissue. The larger branches of the duct lie between the 

 lobules, and constitute the interlobular ducts, giving branches to each lobule which they enter, 



constituting the intralobular' ducts, 



which branch and finally terminate in 

 connection with the alveoli, by means- 

 of an intermediary or intercalary part. 

 The larger interlobar and interlobular 

 ducts consist of a membrana propria, 

 strengthened outside with fibrous and 

 elastic tissue, and in some places also by 

 non-striped muscle, while the ducts are 

 lined by columnar epithelial cells. In 

 the largest branches, there is a second 

 row of smaller cells, lying between the 

 large cells and the membrana propria. 



Fig. 153. Fig. 154. 



Fig. 153. Evolution of glands. A, schema of skin; ep, epidermis; d, cutis with a capillary c; 



B, simple gland with its blood-vessels ; C, D, more complex glands ; E, compound gland, 



blood-vessels omitted. 

 Fig. 154. Rodded epithelium lining the duct of a salivary gland. 



Fig. 155. 



A, duct and acini of the parotid gland of a dog ; B, acini of the sub-maxillary gland of a dog ; 

 c, refractive mucous cells ; d, granular half-moons of Gianuzzi ; C, similar alveoli after 

 prolonged secretion ; D, basket-shaped tissue-investment of an acinus ; F, entrance of a 

 non-medullated nerve-fibre into a secretory cell. 



The intralobular ducts are lined by a single layer of large cylindrical epithelium with the 

 nucleus about the middle of the cell, while the outer half of the cell is finely striated longitud- 

 inally, or u rodded," which is due to fibrillar (fig. 154) ; the inner half next the lumen is 

 granular. The intermediary part is narrow, and is lined by a single layer of flattened cells, 

 each with an elongated oval nucleus. There is usually a narrow "neck," where the intra- 

 lobular duct becomes continuous with the intermediary part, and here the cells are polyhedral.] 

 The acini, or alveoli, are the parts where the actual process of secretion takes place. They 

 vary somewhat in shape some are tubular, others branched, some are dilated and resemble a 



