CHAPTER VII. 



FIG. 60. 



MOUTH DIGESTION. 



The cavity of the mouth is lined by a bright red mucous mem- 

 brane, which is continuous with the skin at the lips. It varies 

 in structure in different parts of the buccal cavity, and in its gen- 

 eral construction more resembles the outer covering of the body 

 than the mucous membrane lining the alimentary tract. It con- 

 sists of (1) an epidermal part composed of thick stratified epithe- 

 lium, the superficial cells of which are flat, scaly and tough, and 

 are placed horizontally, while in the deeper layers the cells are 



soft, rounded or elongated, hav- 

 ing their long axis perpendicular 

 to the surface ; and (2) a deeper 

 part composed of fibro-elastic tis- 

 sue, which, over the alveoli of 

 the teeth, is amalgamated with 

 the periosteum and forms the 

 dense, tough gums. 



The mucous membrane of the 

 mouth is covered with papillse, 

 which on the dorsum of the tongue 

 attain great magnitude and va- 

 riety of shape and epithelial cov- 

 ering. In man, three kinds are described : (1) Narrow pointed, 

 filiform. (2) Blunt and clubbed at the apex, fungiform. (3) 

 Broad complex papillse, circumvallate, surrounded by a fossa, of 

 which there are but a limited number (about a dozen). 



The special secreting organs or glands, which pour their juices 

 into the mouth, have all the same general type of structure, 

 though they vary much in the detail as to the variety and char- 

 acter of their cells. They are known as the aeinous or sacculated 

 glands, from their being made up of numerous acini, or minute 

 elongated sacks or tubules, arranged at the end of a repeatedly 



134 



Diagram taken from a small portion 

 of sacculated gland from Cockroach, 

 showing branching duct and saccules. 



