NUTRITION PROPER. 



293 



Maries, sm, just within the angle of the lower jaw on 

 each side ; and the sublinguals, si, just behind the chin 

 on each side. Every gland has its excretory duct. That 

 of the parotids runs forward and opens into the mouth 

 between the cheek and the upper jaw teeth on each 

 side; that of the submaxillaries runs upward and opens 

 on each side of the back part of the tongue; while that 

 of the sublingual opens on each side of the frenum near 

 the tip of the tongue. 



Structure.— Imagine a slender tube the size of a 

 knitting needle branching and rebranching to capillary 

 fineness, each capillary branch terminating in a saccule, 



ep 



Fig. 179. — Structure of a gland : 1, 2, 3, 4, different stages in the process of 

 infolding of the epithelial surface, ep ; 4, fully formed gland. 



the whole, even to the minutest branch and saccule, 

 lined with a pavement of living nucleated cells, an ex- 

 tension of the epithelium which lines the mouth cavity, 

 then the whole system of tubes webbed together by- 

 loose connective tissue and invested with a membrane 

 of fibrous, or condensed connective tissue, and we have 

 a tolerably good general idea of the structure of a sali- 

 vary gland, which may indeed be taken as a type of a 



