DIGESTION. 57 



8th. The expulsion of the residue, left by the aliments after 

 digestion is finished. 



We will now study successively these different phenomena, and 

 the organs which produce them. 



OF THE PREHENSION OF ALIMENTS. 



17. The first phenomenon of the process of digestion is the 

 prehension of aliments, that is, the act of seizing them and intro- 

 ducing them mto the mouth. 



18. The n out h is a cavity of an oval form, closed in front by 

 the lips, on the sides by the cheeks and jaws, above by the palate, 

 and below by the tongue; behind it is continuous with the pharynx 

 or swallow, but is separated from it by a kind of curtain called 

 the retain jmidit (veil of the palate,) and which may be elevated 

 or depressed so as to close the passage or leave it free. 

 (page OS fig 21.) 



19. The entrance to the mouth may be closed or opened by 

 movements of the jaws and lips On the prehension of aliment, 

 the latter are separated to permit the entrance of the substance, 

 and are immediately afterwards closed to prevent its escape. 



20. With most animals the prehension of aliments is performed 

 by the lips and jaws alone; but with some, other organs are em- 

 ployed to seize the substances and convey them to the mouth. 

 With man and monkeys, the hand thus becomes the chief instru- 

 ment of the prehension of aliments; with the elephant it is his 

 trunk, and with parrots the claw. 



21. With most animals the food remains for some time in the 

 mouth, to be chewed and mixed with saliva. 



OF MASTICATION. 



22. Liquid aliments may be immediately swallowed ; but solid 

 food to be swallowed and digested with facility should be previous- 

 ly divided into very small morsels. 



23 This division, called tttaxticntinu, is effected by the aid of 

 the teeth, which, set in motion by the jaws, press upon the food 

 und cut or crush it. 



17. What is the prehension of aliments? 



18. What is the mouth ? What separates the mouth from the pharynx ? 



19. Is the entrance of the mouth provided with the means of being 1 

 closed or opened 1 



20. How is the prehension o r food effected 1 



21. Docs ilu- food pass at once from the mouth to fie stomach? 



22. May all kinds of aliment he immediately swallowed t 



23. What is mastication 7 How is it effected ? 



5* 



