THE SALIVARY GLANDS. 365 



In studying the organisation of one of these lobules, it will be observed 

 that it is made up of many very small secondary lobules or acini, which are 

 themselves due to the agglomeration of minute elementary vesicles or 

 follicles, whose average diameter is from 1 -500th to 1-1 200th of an inch ; 

 these open into the little canal belonging to each of the secondary lobules, 

 and which again joins those of the other acini of the primary lobule, to form 

 a single duct. 



The minute elementary vesicles or follicles, the glandular culs-de-sac (or 

 ultimate follicles) consist of a thin amorphous membrane (membrana propria), 

 lined by a layer of polygonal epithelium cells. (They are closely sur- 

 rounded by a plexus of capillary blood-vessels). 



When the salivary lobules remain isolated, this canal, which is designated 

 as excretory, because it carries from the lobule the saliva secreted within the 

 elementary follicles, opens directly into the mouth. But when, on the 

 contrary, they all unite and form a single gland, their excretory canals 

 finally converge into one or more principal ducts, whose termination in 

 every case takes place in the same manner by opening into the mouth 

 from the summit of a more or less salient tubercle, an arrangement which 

 Fig. 169. Fig. 170. 



LOBULE OF PAROTID GLAND, INJECTED WITH CAPILLARY NETWORK AROUND THE FOLLI- 

 MERCURY, AND MAGNIFIED 50 DIAMETERS. CLES OF THE PAROTID GLAND. 



renders the introduction of particles of food into these excretory orifices 

 somewhat difficult. The fibrous and elastic walls of these ducts are lined 

 internally by columnar epithelium. 



If to the fundamental tissue just described, be added arteries, veins, and 

 lymphatics, which convey the materials of secretion and nutrition, as well as 

 the nerves which regulate the secretory and nutritive acts, all the elements 

 entering into the organisation of the salivary glands are made known. 



The most voluminous of these glands or those which comprise a very 

 great number of agglomerated lobules, will be first noticed. They are 

 the parotid, maxillary, sublingual, and molar glands, which are all pairs, and 

 are placed in proximity to the mouth when they do not lie immediately 

 beneath the adherent face of its mucous membrane. Secondly, the less im- 

 portant glands those which are spread in layers under that membrane, and 

 including the labial, lingual, and palatine glands, will be examined. 



1. Parotid Gland. (Figs. 110 ; 172, 8). 



Preparation. This gland, with its excretory canal, is seen after the removal of the 

 cervicofacial subcutaneous and parotido-auricularis muscles. 



The parotid gland is situated in the space included between the posterior 



