GENERAL CHARACTERS OF MAMMALIA. . 25 



There are too, some mammalia, having extremities formed for 

 running, or for climbing solely, that can also sustain themselves 

 for a short time in the air by the assistance of a fold of skin 

 which extends between the posterior and anterior paws, consti- 

 tuting a sort of parachute; (Plate 4, Jig. 8.) but this mode of 

 organization does not give them the power of actually flying, like 

 those above described. 



19. Of all animals, the mammalia have most intelligence, 

 and they also possess the most voluminous brains. But in this 

 respect they present very striking differences amongst themselves, 

 and it is generally remarked, they are less favored in this parti- 

 cular, in proportion as they depart in resemblance from man, as 

 their forehead is more retreating, and the face or snout, more 

 projecting. 



20. There also exists, very great differences among the mam- 

 malia as respects their teeth; and as the conformation of these 

 organs is always in relation to the kind of food upon which the 

 animal is destined to feed, we will say a few words about them. 



2 1 . Some mammalia that feed upon soft insects, (as ants,) or 

 on very small fishes which they can swallow whole, are desti- 

 tute of teeth; but almost all animals of this class possess teeth 

 designed for the division of food. The molar teeth are gene- 

 rally the most useful, and their presence is more constant than that 

 of the incisor or canine teeth ; the latter are necessary to seize 

 and divide a living prey, and consequently are not wanting in 

 any carnivorous animal ; but they are less useful to herbivorous 

 animals, and the one or the other kind is absent in most mammalia 

 that live upon vegetable diet. Sometimes, too, they afford no 

 assistance in mastication, though very much developed, and con- 

 stitute a more or less powerful means of defence. The form of 

 the molar teeth varies according to the food of the animal. 



22. In those animals that live upon flesh, the molars are com- 

 pressed and cutting, and so arranged as to act one against the other 

 like the blades of a pair of scissors; (Plate 2, fig. 12.) in those 

 which feed upon insects, these teeth are studded with contig- 



19. What class of animals possc.-s the largest brains ? Is the brain of the 

 same size in all the mammalia? 



20. Are the teeth of all the mammalia the same ? 



21. Are any of the mammalia destitute of teeth ? What kind of teeth is 

 most generally present in the mammalia ? In what family of animals are 

 the incisor and canine teeth always present ? Does the form of the molar 

 teeth depend upon the kind of food upon which the animal feeds? 



22. What is the form of the molar teeth in tho-e animals that feed on flesh/ 

 What are the peculiarities of the teeth of animals that feed on insects ? What 

 are the peculiarities of the teeth of animals that feed on vegetables and 

 fruits ? 



