116 FOSSIL MAMMALIA. 



form to another is so gradual, and the functions of one species 

 receive such ample and obvious illustrations from those of 

 the species adjacent to it, that we are rarely at a loss, to 

 see the final cause of almost every arrangement that is pre- 

 sented to the anatomist. This is more especially the cas^ 

 with respect to the skeleton, which forms the foundation of 

 all the other mechanisms within the body, and is of the 

 highest importance in the history of fossil animals, of which 

 we rarely find any other remains besides the bones, and 

 teeth, and the scaly or osseous integuments. I select the 

 Megatherium, because it affords an example of most extra- 

 ordinary deviations, and of egregious apparent monstrosity ; 

 viz. the case of a gigantic animal exceeding the largest 

 Rhinoceros in bulk, and to which the nearest approxima- 

 tions that occur in the living world, are found in the not 

 less anomalous genera of Sloth, Armadillo, and Chlamy- 

 phorus ; the former adapted to the peculiar habit of residing 

 upon trees ; the two latter constructed with unusual adapta- 

 tions to the habit of burrowing in search of their food and 

 shelter in sand ; and all limited in their geographical distri- 

 bution, nearly to the same regions of America that were once 

 the residence of the Megatherium. 



I shall not here enter on the unsettled questions as to the 

 precise age of the deposites in which the Megatherium is 

 found, or the causes by which it has been extirpated ; my 

 object is to show that the apparent incongruities of all its 

 parts, are in reality systems of M'ise and well contrived adap- 

 tation to a peculiar mode of life. I proceed therefore to 

 consider, in the order in which they are described by Cu-- 

 vier, the most important organs of the Megatherium, be- 

 o-inning with the head, and from thence advancing to the 

 trunk and extremities. 



Head. 



The bones of the head (PI. 5, Fig. 1. a.) most nearly re- 



