CH. xxx.] SALIVA. 471 



CHAPTER XXX. 



SALIVA. 



THE saliva is formed by three pairs of salivary glands, called 

 the parotid, submaxillary, and sublingual glands. 



The Salivary Glands. 



These are typical secreting glands. They are made up of 

 lobules united by connective tissue. Each lobule is made of a 

 group of tubulo-saccular alveoli or acini, from which a duct 

 passes; this unites with other ducts to form larger and larger tubes, 

 the main duct opening into the mouth. 



Each alveolus is surrounded by a plexus of capillaries ; the 



Fig- .19.1- -From a wetion through a salivary gland, a, HCTOIIH or albuminous alveoli ; 

 b, intralobular duct cut transversely. (Klein and Noble Smith.) 



lymph which exudes from these is in direct contact with the 

 basement membrane that encloses the alveolus. The basement 

 membrane is lined by secreting cells which surround the central 

 cavity or lumen. The basement membrane is thin in many 

 places to allow the lymph more ready access to the secreting 

 cells : it is continued along the ducts. 



The secreting epithelium is composed of a layer of polyhedral 

 cells. 



The epithelium of the ducts is columnar, except where it passes 

 into an alveolus ; at this point it is flattened. The columnar 

 epithelium cells of the ducts exhibit striations in their outer part 

 (see fig. 393) ; the inner zone of each cell is made of granular proto- 



