DIGESTION. 



another. They are compound' tubulo-alveolar glands composed of 

 small irregularly shaped lobules united by areolar tissue and con- 

 nected by branches of the salivary ducts. Each lobule is made up of 

 a number of small alveoli or acini more or less tubular in shape which 

 are the terminal expansions of the smallest ducts. (See Fig. .62.) 

 The wall of the acinus is formed by a reticulated basement mem- 

 brane, surrounded externally by blood-vessels, the spaces between 

 which constitute lymph-spaces or channels. The inner surface of 

 the acinus membrane supports a single layer of irregular spheric 

 or polygonic epithelial cells. The cells do not entirely fill up the 

 cavity of the acinus, but leave an intercellular space, the lumen, 

 which constitutes the beginning of the duct for the transmission of 

 the secretion to the mouth. From 

 each acinus there passes a narrow 

 intercalary duct lined by a layer of 

 flattened cells. The common ex- 

 cretory duct formed by the union 

 of the intralobular and interlobular 

 ducts consists also of a basement 

 membrane, lined, however, by tall 

 columnar epithelial cells. The sali- 

 vary glands are abundantly supplied 

 with blood-vessels and nerves which 

 are closely related to their activity. 



Based partly on the character 

 of their secretions and partly on 

 the microscopic appearance of their 

 secreting cells, the salivary glands 

 have been divided by Heidenhain 

 into two classes: viz., j^r/jus or al- 

 buminous, and mucousr gBjjids . To 

 the first class beloftg" the parotid, a 

 portion of the submaxillary, and a portion of the glands of the 

 tongue. To the second class belong a portion of the submaxillary 

 gland, the sublingual, a portion of the glands of the tongue, the glands 

 of the cheeks, lips, palate, and pharynx. It is possible that a single 

 alveolus of any gland may contain both albuminous and mucous 

 cells. 



In the serous glands the cells are more or less spheric in shape, 

 nucleated, and almost completely filled with dark granular material 

 (Fig. 63). In the mucous glands the cells are large, clear in appear- 

 ance, and loaded with a highly refracting material resembling mucin 

 (Fig. 64). Between the basement membrane and the clear cells are 

 to be found in the acini of the submaxillary glands small crescentic 

 shaped cells filled with granular material which stains deeply with vari- 



Acini. 



FIG. 62. SCHEME OF THE HUMAN 

 SUBMAXILLARY GLAND. 



