GENERAL CHARACTERS. 203 



The foregoing are almost the only characters common to the whole of the 

 Edentates. It may be added, however, that all these animals are of a comparatively 

 low degree of organisation, although many of them are specialised for particular 

 modes of life. In general their brains are relatively small, with the hemispheres, 

 or anterior portion, devoid of convolutions, and not extending backwards to overlap 

 and conceal the hinder portion or cerebellum. In some cases, however, the hemi- 

 spheres of the brain are distinctly convoluted. Very frequently the shoulder-blade, 

 or scapula, is characterised by the great development of the anterior portion of its 

 lower extremity ; this so-called coracoidal portion (of which we shall have to speak 

 more fully when we come to the Egg-laving .Mammals), being sometimes, as shown 

 in our figure of the skeleton of the sloth, marked off from the remainder of the 

 bone by a perforation, and suturally united with it. Certain members of the order, 

 such as the armadillos and their extinct allies, are peculiar among Mammals in 

 possessing a bony cuirass in the skin : while the pangolins are equally remarkable 

 for the coat of overlapping horny scales with which the entire body is invested. 



From the absence of enamel in their teeth, and the presence of rudimental 



milk-teeth in some of their representatives; it is probable that the Edentates should 



be regarded as somewhat degenerate types, descended from ancestors provided 



with a double set of enamel-coated teeth. There are, however, no indications of 



any close relationship between the Edentates and any other of the Mammalian 



orders; and it is accordingly pretty evident that they are descended from extinct 



primitive Mammals quite independently of all other members of the class. 



As already mentioned,, the sloths, ant-eaters, and armadillos, are 

 Distribution. . P -, ^- m 1 • • • 



entirely confined to the New \\ orld : and since it is these alone which 



form the typical Edentates, the order is essentially an American one. Indeed, 



there is a considerable degree of doubt whether the Old World pangolins and 



aard-varks, which form its only other representatives, are rightly included within 



the order; their organisation being very different from that of the typical forms. 



Be this as it may, the typical Edentates appear to have been always confined 



to the New World, in the southern half of which they attained their greatest 



development ; for while fossil forms are abundant in America, they are unknown 



elsewhere. 1 Some of these extinct types are of the greatest importance to the 



zoologist, since they serve to connect together most intimately such widely different 



forms as the arboreal sloths and the terrestrial armadillos. 



Although varying greatly in their mode of life, the whole of the 

 Mode of Life. ^ ... 



Edentates — both living and extinct — are either arboreal or terrestrial, 



none of them being modified either for flight in the air or for swimming in the 



water. While the purely arboreal sloths are entirely vegetable feeders, all the 



other members of the order, of which a few are likewise more or less arboreal in 



their habits, subsist on flesh or insects. Moreover, several of these carnivorous 



forms are burrowing animals; and it is remarkable that the members of three 



distinct groups, namely, the ant-eaters, the pangolins, and the aard-varks, subsist 



mainly, or exclusively, on white ants or termites ; the only other purely ant-eating 



members of the class belonging respectively to the Pouched Mammals and the Egg- 



1 Certain remains from the Tertiary rocks of France have been considered to belong to armadillos, but this 

 determination is exceedingly doubtful. 



