190 



HISTOLOGY. 



empty cells are smaller than the others, and the nuclei, though at the base 

 of the cell and transversely oval, are not as flat as in cells full of secretion. 

 Seldom can cells be found completely occupied by unaltered protoplasm. 

 A single gland, or even a single alveolus, may contain cells in different 

 phases of secretion, as is clearly seen when special mucin stains are used. 

 Secretory capillaries are not found in the purely mucous glands. 



Mixed Glands. 



The mixed oral glands are the sublingual, submaxillary, anterior lin- 

 gual, labial, buccal, and molar glands. They all possess crescents of serous 

 cells such as are to be described in the largest glands of this gro'up, the 

 sublingual and submaxillary. 



Excretory 

 duct. 



Crescents. 



End pieces. 





Secretory duct. 



f&* Blood vessel 



FIG. 214. DIAGRAM OP THE 

 HUMAN SUBLINGUAL GLAND. 



FIG. 213. SECTION OP THE SUBLINGUAL GLAND FROM A MAN 

 OP 23 YEARS. X 80. 



The sublingual glands are two groups of glands, one on either side of 

 the median line, under the mucous membrane in the front of the mouth. 

 The largest component is an alveolo-tubular structure emptying by the 

 ductus sublingualis major on the side of the frenulum linguae. The main 

 stem and the principal branches of the large sublingual duct are lined by , 

 a two-layered or pseudostratified columnar epithelium, as in the parotid 

 duct. They are surrounded by connective tissue containing many elastic 

 fibers. Ducts less than .05 mm. in diameter have a simple columnar 

 epithelium, which in a few places becomes low and basally striated to form 

 the secretory ducts (also called salivary ducts). As shown in the dia- 

 gram, Fig. 2 14, the secretory ducts are very short, and narrow intercalated 

 ducts are absent. The tubules are surrounded by basement membranes 



