8 ON THE STRUCTURE AND 



are surrounded on all sides by fat, which is also spread be- 

 twixt their bundles of fibres, and betwixt the small fibres 

 themselves, which lie contiguous to each other. This fat, 

 being pressed out by the turgescence of the muscles and 

 their fibres, tends to render them soft, flexible, slippery, 

 and fit for motion : and gives to the body its softness and 

 beauty, at the same time also that it protects from injury, 

 and keeps warm several of the more tender parts. 



The Organs of Nutrition. 



The function of nutrition commences in the mouth, info 

 which the aliments are taken, and where, when they are 

 solid, they are masticated, and moistened with the saliva. 

 From thence they are passed into the alimentary canal for 

 digestion i Mastication is performed by the teeth, aided by 

 the motion of the tongue. The jaws are horizontal, and^ 

 the mouth always ojfens, by their separation, from the front 

 backwards. The teeth are inserted into cavities or sockets 

 of the jaws. They consist of three different substances; of 

 the proper matter or ivory, of bone, and of enamel. The 

 ivory is produced from a pulpy, vascular matter, situated 

 in the base of the sockets ; and the enamel, which covers 

 their upper external surface, is supposed to be a species of 

 crystallization, and is arranged in regular since. According 

 to their situation in the mouth, they are denominated front- 

 teeth, canine-teeth, or grinders. In their number and shape 

 they are, of course, different in different animals. 



The front-teeth, called also cutting-teeth, and incisors^ have, 

 in Men and Apes, a broad and sharp edge. In the Lemurs, 

 and most predatory animals, they are sharp pointed. In the 

 Dogs they are lobateJ. In the upper jaws of the Squirrels 

 they are wedge-shaped, and in the under jaws compressed. 

 In the Hares, Rats, and several others, they are long and 



subulated. 



