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 presented to the anatomist. This is more especially the case 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 extraordinary deviations, and of egregious apparent monstrosity; viz. the case of a gigantic animal exceeding the largest Rhinoceros in bulk, and to which the nearest approximations that occur in the living world, are found in the not less anomalous genera of Sloth, Armadillo, and Chlamyphorus; the former adapted to the peculiar habit of residing upon trees; the two latter constructed with unusual adaptations to the habit of burrowing in search of their food and shelter in sand; and all limited in their geographical distribution, 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 wise and well contrived adaptation to a peculiar mode of life. I proceed therefore to consider, in the order in which they are described by Cuvier, the most important organs of the Megatherium, beginning with the head, and from thence advancing to the trunk and extremities.
Head.
The bones of the head (Pl. 5, Fig. 1. a.) most nearly resemble
