1 84 



ELEMENTS OF HISTOLOGY. [Chap. xxn. 



from the crescent cells. This is improbable, since, 

 during ordinary conditions of secretions, there is no 

 disappearance of the mucous cells as such ; they change 



in size, be- 

 coming 

 during 



larger 

 secre- 



tion, and their 

 contents are 

 converted into 

 perfect mucus. 

 It is probable 

 that, on pro- 

 longed exhaus- 

 tive stimula- 

 tion, the mucous 

 cells collapse 

 into the small 

 cells, seen by 

 I03.-From a Section through the Orbital Heidenhainand 



land of Dog, after prolonged electrical his pupils. 



^ 



alveoli of the 

 sub -lingual of 



the dog are again different in structure both from those 

 of the sub-maxillary of the dog and of the sub-lingual 

 of guinea-pig, for the alveoli are there lined either 

 with mucous cells or with columnar albuminous 

 cells, or the two kinds of cells follow one another 

 in the same alveolus. 



This gland is a sort of intermediate form be- 

 tween the sub-lingual of man and the sub-maxillary 

 of man and ape, i.e., the mixed or muco-salivary 

 glands. In these the great number of alveoli are 

 serous, i.e., small, with small lumen, and lined witli 

 albuminous cells, whereas there are always present 

 a few alveoli exactly like those of a mucous gland. 

 The two kinds of alveoli are in direct continuity with 



stimulation. 

 The alveoli are lined with small granular cells. 



