Chap, xxii.] THE SALIVARY GLANDS. 185 



one another. In some conditions there are only very 

 few mucous alveoli to be met with within the lobule, 

 so few sometimes that they seem to be altogether 

 absent ; in others they are numerous, but even under 

 most favourable conditions form only a fraction of the 

 number of the serous alveoli. In the sub- lingual of 

 man they are much more frequent, and for this reason 

 this gland possesses a great resemblance to the sub- 

 lingual of the dog. 



What appear to be crescents in the mucous alveoli 



Fig. 109. Alveoli of Serous Gland. 

 A, At rest ; B, first stage of secretion ; c, prolonged secretion. (Langley.) 



of the human gland are an oblique view of albuminous 

 cells lining the alveoli at the transition between the 

 mucous and serous part of the same gland-tube. 



247. The columnar salivary cells lining the alveoli 

 of the sub-maxillary of the guinea-pig in some condi- 

 tions show two distinct portions, an outer homogeneous 

 or slightly and longitudinally striated substance, and 

 an inner, more transparent, granular-looking part, and 

 in this respect the cells resemble those of the pancreas. 

 (See a future chapter.) 



Langley has shown (Fig. 109) that during the 

 period preparatory to secretion the cells lining the 

 alveoli of the serous salivary glands become enlarged 



