XXIII.] THE SALIVARY GLANDS. 2 57 



Serous Salivary Glands. The parotid of man and mammals, 

 and the sub-maxillary of the rabbit. 



Mixed or Muco-Salivary. The human sub-maxillary, retro- 

 lingual of the dog, or sub-maxillary of the guinea-pig. 



The salivary glands are compound tubular glands, i.e., the duct is 

 branched, while the acini or alveoli the true secretory parts of 

 the glands are tubular in form. Each gland consists of lobes, 

 held together by connective tissue, which forms a capsule for the 

 whole gland and gives septa to enclose the lobes and lobules. 

 Each lobe in turn is made up of numerous smaller lobules also held 

 together by connective tissue, which carries the blood-vessels, 

 nerves, lymphatics, and larger ducts. From mutual pressure the 

 lobes and lobules are usually polygonal in shape. The main duct 

 is made up by the convergence of ducts from the lobes lobar 

 ducts while from each lobule there is a duct lobular ducts, 

 which unite to form lobar ducts. Each lobule is made up of a 

 number of alveoli or acini. Each alveolus, which has a closed 

 extremity, leads into or discharges its secretion into a fine duct or 

 ductule, and these ductules by their union form the intralobular 

 ducts. Practically the arrangement of the ducts is the same in all 

 this set of glands ; the diiferences in structure are in the alveoli. 

 The alveoli consist of a basement membrane, which by appro- 

 priate means can be shown to consist of branched cells forming a 

 reticulated or basket-like membrane. This is lined internally by 

 the secretory epithelium, leaving a larger or smaller lumen in the 

 centre, \vhich leads into a fine duct or ductule by means of a narrow 

 functional piece or intermediary part or ductule, in which the epi- 

 thelium is somewhat flattened. Usually several alveoli open into 

 one intermediary tubule or ductule. The ducts with a fibrous wall 

 are lined by a single layer of columnar epithelium, which is striated 

 or " rodded " in its outer part, and granular towards the lumen of 

 the tube (fig. 249); a little inwards from the centre of each cell is 

 a nucleus. 



In mucous glands the acini (35 p, in diameter) are lined by a 

 layer of polyhedral clear cells, whose broader bases rest on the 

 basement membrane, while their apices abut on the lumen, which 

 is small (fig. 249). Usually in a transverse section of an acinus 

 five or six cells are seen. The appearance of these cells varies 

 according as a gland is at rest or in a state of activity, i.e., whether 

 the gland is "loaded" or "charged" (resting phase), or "unloaded" 

 or "discharged" (active phase). In a resting gland the mucous 

 cells are clear, for the most part, while at the outer part of the cell 

 is a flattened nucleus surrounded by a very small quantity of 

 granular protoplasm. The clear part is traversed by a network of 

 fibrils, which includes in its meshes mucigen. The granular matter 



