66 ON THE PLACE OF MAN IN THE SCALE OF BEING. 



the peculiar structure of the teeth, which consist of alternating plates of ena- 

 mel, ivory or dentine, and cementum or crusta petrosa, substances of three 

 different degrees of hardness ; and, as the softer portions will of course wear 

 down first, the harder remain as projecting ridges. In order to give effect to 

 these, there is usually a considerable power of lateral motion possessed by 

 the lower jaw ; so that a regular grinding action may be performed, which is 

 favourable to the complete reduction of the tough vegetable substances that 

 serve as their food. 



49. Animals with Unguiculated fingers are capable of more variety in the cha- 

 racter of their food. In some it is almost exclusively vegetable, as in the Roden- 

 tia ; and here the power of prehension possessed by the extremities is small, 

 the fore-arm not being so constructed as to be capable of the motions of pro- 

 nation and supination. In this order, the mouth is remarkably adapted for 

 grinding down hard vegetable substances ; the molar teeth being furnished with 

 transverse ridges of enamel; and the jaws having a powerful movement back- 

 wards and forwards.* In other orders, again, there is an almost exclusive adap- 

 tation to animal food. The toes are furnished with long and sharp claws ; 

 and the fore-feet may be placed in a variety of positions, by the rotation of 

 the two bones composing the lower part of the leg. The grinding teeth are 

 very narrow, and are formed with sharp points and edges, so as to be adapted 

 for dividing animal flesh ; these are firmly set in short strong jaws, which are 

 fitted together like the blades of a pair of scissors, having no action but a 

 vertical one ; and the constant friction of the edges of the molar teeth against 

 each other, keeps them sharp.t In the Carnivorous group, too, we find the 

 greatest development of the canine teeth, which are commonly absent or but 

 slightly developed among herbivorous quadrupeds ; these are instruments of 

 great power, serving both for the first attack of their prey, and for subse- 

 quently tearing it in pieces. It is evident that the whole structure of the body 

 must undergo modification, in conformity with the nature of the food. The 

 simple stomach and intestinal canal of the Carnivorous animal, adapted only 

 to the digestion of aliment consisting of materials similar to those of its own 

 body, would be totally useless to an animal prevented by its general organi- 

 zation from obtaining any other than vegetable food ; and, on the other hand, 

 the teeth and hoofs of the Herbivorous quadruped would be of little assist- 

 ance to an animal, whose instincts and general conformation adapted it for the 

 pursuit of animal prey. It will be presently seen that, in regard to his or- 

 ganization, Man holds an intermediate place between the purely Herbivorous 

 and the purely Carnivorous tribes ; being capable of subsisting exclusively 

 upon either kind of diet, but being obviously intended by Nature to employ 

 both in combination. 



50. The classification of the Mammalia by Linnaeus, although not strictly 

 natural, affords us the readiest means of separating Man, zoologically, from all 

 other animals. He arranged under his order Primates, all the unguiculated 

 Mammalia which have four incisor teeth and two canines in each jaw; and 

 thus Man, with the Monkeys and the Bats, was distinguished from the re- 



' The action of trituration is chiefly performed by the external pteregoid muscles. When 

 these are in operation together, they draw the whole of the lower jaw forwards, so as to 

 make the lower teeth project beyond the upper; and the jaw being dnuvn back again by 

 the digastric nmsrlcs, a rapid alternate movement maybe thus effected, such as is seen in the 

 Rodcntia. When only the muscle of one side acts, the condyle of that side is thrown for- 

 wards; and by the alternating operation of the two, aided by other muscles, that rotatory 

 motion is given which we see especially in Ruminating Quadrupeds. 



| In Carnivorous animals, the muscles which elevate the lower jaw attain a very high 

 degree of development. This is very remarkably seen in the internal pteregoid, which in 

 Alan is of subordinate size and importance, but which is a very powerful muscle in the Lion, 

 Tiger, &c. 



