126 INTRODUCTION. 



food, nor even divide it into morsels, as the feline animals do, but seize it 

 with a snap, and swallow it in an instant : to the office of seizing and re- 

 taining the slippery agile prey, upon which they feed, the teeth and jaws 

 of these aquatic tyrants are specially adapted. Eager as a hound in 

 the chase, they pursue, with relentless pertinacity, the shoals of fishes, 

 whose numbers they greatly thin ; for their appetite is voracious, and their 

 digestion rapid. 



Thus, then, is the structure of the articulation of the lower jaw 

 consistent with the characters of the teeth, which are themselves modi- 

 fied according to the food upon which the animal is destined to subsist. 

 Where a grinding, mill-like action of the teeth is required, the articu- 

 lation is so fashioned as to give to the jaw the due degree of mobility ; 

 but where the action is simple, and scissor-like, or where the jaws are 

 destined to hold living prey, struggling within their vice-like gripe, there 

 the articulation is limited in its sphere of motion, and strengthened to 

 endure the strain thrown upon it by the efforts of the muscles. 



ON THE DIGESTIVE ORGANS, AND THEIR APPENDAGES. 



THE digestive apparatus in the Mammalia, the due and healthy action 

 of which is essential to the well-being of the individual, is so compli- 

 cated and curious, as to demand a notice of it at some length : more 

 especially, as it presents certain modifications, in various groups of ani- 

 mals, important to be understood by the naturalist who would know 

 something more of living bodies than their external form, and superficial 

 characters. The digestive canal commences with the mouth ; and the 

 teeth are the first agents in the reduction of the food to a state proper for 

 transmission to the stomach. From the mouth, a muscular tube, the 

 oesophagus, leads to the stomach, in which the digestive process takes 

 place : to this succeeds the intestinal canal ; during its course through 

 which, the digested mass, or chyme, is subjected to the absorbing action 

 of the lacteals, or chyliferous vessels, which take up the nutritious por- 

 tion, or chyle, and ultimately convey it to the heart, to be mingled with 

 the blood. Where the food is of a vegetable nature, or abounds with 

 an inferior portion of nutriment, the stomach and intestinal canal are far 

 more complex than in truly carnivorous animals, in which the stomach is 

 simple, and the intestinal canal short ; for the more highly animalized (if 

 the word may be allowed) the food, the more replete is it with nutriment, 

 and the more easily is that nutriment extracted. 



The food of Mammalia consists of herbage, fruits, grain, and other 

 vegetable matter ; of molluscous animals, worms, insects, fishes, reptiles, 

 birds, and also of other Mammalia, 



