STRUCTURE OF THE SALIVARY GLANDS. 



1587 



breaks up into delicate rod-like processes, in recognition of which the cells lining the 

 intralobular tubules are often designated rod-epithelium. An active secretory role 

 has been ascribed to these cells, R. Krause ^ having succeeded in demonstrating an 

 excretory function by means of sodium sulphindigotate. The interlobular and inter- 

 lobar ducts gradually increase in size and possess a lining of columnar cells which are 

 usually arranged as a single layer. In the larger canals, however, the epithelium 

 consists of two imperfect rows, since smaller cells lie next the basement membrane, 

 wedged in between the larger typical elements. The columnar cells continue until 

 near the termination of the main excretory duct, where they give place to the stratified 

 squamous epithelium prolonged from the oral mucous membrane. 



Fig. 1347 



Intermediate duct 



Tubular alveolus 



fe- -^,. Alveolar lumen 



Interlobular duct 





Section of parotid gland, showing serous alveoli. X 270. 



The submaxillary gland differs in structure from the parotid in possessing 

 both serous and mucous alveoli, the latter forming approximately one-fifth of the 

 entire organ. The alveoli containing serous cells correspond closely with those of 

 the parotid, being from .020 to .030 mm. in diameter and filled with elements loaded 

 with minute granules. Not infrequently the cells exhibit differentiation into an inner- 

 granular and an outer almost granule-free zone. The mucous alveoli are often some- 

 what larger than the serous, reaching a diameter of .040 mm. or more. The mucus- 

 producing cells present the usual appearance and share the acinus with typical demi- 

 lunes consisting of cells identical with those lining the serous alveoli. The mucous 

 acini are directly connected with those of the serous type. 



Intermediate tubules connect alveoli of both kinds with the intralobular canals; 

 those beginning in mucous acini are shorter (.035-. 060 mm.) and less richly branched 

 than the tubules originating in serous alveoli. The latter measure from .060-. 140 

 mm. in length, and repeatedly divide ; they are lined with low cubical cells which are 

 gradually transformed from the alveolar epithelium in contrast to the abrupt transition 

 seen in the tubules connected with mucous acini. The cells lining the intralobular 

 tubules of the submaxillary gland exhibit the characteristic rod-like striation seen in 

 the parotid, the rod-epithelium sometimes containing yellowish pigment granules. 

 The interlobular and interlobar ducts resemble those of the parotid gland. The 

 chief excretory duct possesses, in addition to a subepithelial elastic layer, a weakly 

 developed stratum of longitudinally disposed involuntary muscle. Goblet-cells appear 

 between the columnar elements lining the duct. 



The sublingual gland, being of the mixed mucous type, resembles in structure 

 the labial and buccal glands, and consists of a series of individual lobules, opening by 

 half a dozen or more separate ducts, rather than a compact single organ. In com- 



* Archiv f. mikro. Anat., Bd. xlix., 1897. 



