138 



Physiological Summary. 



In the foregoing pages it has been my aim to place the new facts yielded by 

 the study of the skeleton of the Mylodon in a clear and intelligible light, and in 

 their true relations to those before acquired in the osteology of existing and extinct 

 Edentate animals : I now proceed to endeavour to deduce the consequences 

 which necessarily and legitimately flow from them ; as without this additional, 

 and, as in all similar cases, most difficult task, the full value and meaning of the 

 phenomena would not perhaps be fully comprehended. 



That animals with the same dental structure have the same kind of food is a 

 well-established and safe physiological inference, at least as applied to members 

 of the class Mammalia, and more especially to those in which the modifications of 

 the teeth are of an extreme nature, as in the strictly carnivorous and herbivorous 

 famihes. Yet this rule, from which all the other physiological consequences flow in 

 the interpretation of the remains of extinct animals, requires much caution in its 

 application. In the Ruminantia, for example, which are remarkable for the uni- 

 formity of their peculiar dentition, there exists a certain range of variety in their 

 vegetable food : most of the species feed on grass ; others browse as well as 

 graze, and combine with herbage the buds and leaves of trees ; one genus {Came- 

 lopardalis) subsists exclusively on foliage ; another {Rangifer) on lichens. 



The Sloths, however, are characterized by a dentition still more peculiar and 

 extreme in its modifications than that of the Ruminants, and this character is 

 apparent not only in the form, number, and general composition, but also in the 

 intimate structure and mode of growth of their teeth, which are especially adapted 

 for acting on the tender buds and leaves of trees. And since we have seen that 

 all the dental characters of the Sloths coexist in the extinct Megatherioids with 

 the bradypodal modifications of the jaws and cheek-bones, implj'ing the same 

 development and disposition of the masticatory muscles, we cannot but con- 

 clude that these concurrent conditions of dental and maxillary organs must have 

 related to the comminution of the same vegetable substances. 



But the few large quadrupeds which at the present day derive the whole or a 

 chief proportion of their sustenance from trees, present very remarkable modi- 

 fications of organic structure in relation to the acquisition of such food : and the 

 inference above deduced from the teeth and jaws of the Megatherioids ought 



