DIGESTION 



147 



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 excretory 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 salivary 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 micro- 

 scopic appearance of their secreting cells, the salivary glands have been 

 divided by Heidenhain into two classes: viz., serous or albuminous, and 

 mucous glands. To the first class belong the parotid, a portion of the sub- 

 maxillary, 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 albu- 

 minous and mucous cells. 



FIG. 62. PAROTID GLAND AT REST. 1,1, 

 Acini; 2, duct; 3,3, albuminous cells filled 

 with fine granules; 4,4, nuclei almost con- 

 cealed. (Semi-diagrammatic.) 



FIG. 63. SUBMAXILLARY GLAND AT 

 REST. 1,1, Acini; 2, duct; 3, 3, mucous cells 

 containing mucin; 4,4, nuclei, flattened and 

 dispersed toward the base of the cells; 5,5, 

 crescents of Giannuzzi. (After Vialleton^ 



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

 and almost completely filled with dark granular material (Fig. 62). In the 

 mucous glands the cells are large, clear in appearance, and loaded with a 

 highly refracting material resembling mucin (Fig. 63). Between the base- 

 ment membrane and the clear cells are to be found in the acini of the sub- 

 maxillary glands small crescentic shaped cells filled with granular material 

 which stains deeply with various coloring matters. These are known as 

 the demilunes of Heidenhain. At one time it was supposed that they were 

 young cells destined to take the place of the clear cells which were believed 

 to be exhausted and to have undergone disintegration. At the present time 

 they are regarded as albuminous or serous cells which exhibit changes 

 similar to the cells of the parotid gland. 



The glands embedded in the mucous membrane covering the tongue, 

 lips, cheek, palate, and pharynx are for the most part lined with epithelial 

 cells which contain a highly refracting matter similar to, if not identical with, 

 that found in the cells of the submaxillary and sublingual glands. 



