mous body is preserved in a skeleton existing in the Museum at Madrid. Another skeleton, also, of a nearly allied species (Mylodon*), smaller indeed, but not less interesting, has been brought to England, and has been the subject of a most elaborate description by Professor Owen, while the skeleton itself, admirably articulated, may be seen in the Museum of the Royal College of Surgeons in London. The complete structure of an extinct species has in no instance been more satisfactorily made out than in the case before us; and, therefore, the whole nature Fig. 145

of the argument by which conclusions are arrived at, from the comparison of the shapes and peculiar projections and proportions of bones, may well be illustrated here by a reference to this remarkable extinct species.

Muλn (myle), a mill; odovç (odous), a tooth.

First of all, let us take a general view of this extraordinary animal, whose singularly massive proportions cannot but strike every one with astonishment.* Its length is nineteen feet, its breadth across the loins nearly six feet, its height not more than nine. The general proportions of the body rather resemble those of the hippopotamus than the elephant; and the trunk itself, much larger than that of any hippopotamus, is terminated by a pelvis, and by hind extremities nearly three times as large as those of the most gigantic elephant. These hind-legs are provided with feet set at right angles to the leg, as in the bear; the heel projects nearly fifteen inches backwards, and the toes, armed with claws, proceed more than twice that distance forwards, so that a proper base is afforded for the massive column, and the whole is able to sustain the weight that once rested upon it. There is also, in addition to the hind legs, a tail more than equal to them in length, and proportionally thick and strong; and this tail must have supported, instead of depending from the broad termination of the pelvic region.

To match these strange proportions of the hinder extremity, we find the fore-legs longer than the corresponding part in the hind limb, but having a perfect mechanism for free motion in all directions, and connected to the sternum by a very powerful bony apparatus, also permitting free motion. This extremity was terminated by unusually broad expanded

* See the figure of the skeleton in the preceding page, where the proportions will be recognised on comparing the figure with that of an ordinary-sized man, drawn to the same scale and placed by the side for this purpose.

feet, of which the proportions, however, are much reduced in appearance, in consequence of the massiveness of the leg itself, already described. The foot is five-toed; the two outer toes were provided with claw bones of great size and strength, but the whole foot is short in proportion to its breadth.

The skull of this strange monster was exceedingly small and narrow, and was connected to the trunk by a neck of moderate length. The whole body gradually tapers forward from the enormous pelvis and gigantic hind-quarters, which offer a singular contrast to the short neck and slender head. These singular proportions are nowhere met with amongst quadrupeds, except amongst the Edentata, of which the Megatherium is certainly one of the most interesting examples.

Let us now trace the points of analogy that exist between the Megatherium, or rather the megatheroid animals, including under this name the various gigantic species of the same group at present known, and the sloth, the living animal most nearly allied to them.

The first glance at the head of the Megatherium exhibits very striking resemblances to the sloth in several points, some of them peculiar to the whole tribe of edentates, and others indicative of the habits of the animal. The general form is more elongated and straighter, the length however not being due to the prolongation of the jaws (which are cut off shortly), but to the skull itself; and the structure of the bones of the nose would seem to indicate the existence of a long upper lip, or even a short proboscis. The extreme narrowness of the palate is also worthy of notice, and was, no doubt, in accordance

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with peculiar habits. The long broad bone, descending by the side of the cheek, is one of those points in which the resemblance to the sloth is carried out very accurately; and this is not less interesting, although we are at present ignorant of its exact meaning. It is characteristic of the whole group of Eden

tata.

The teeth of the megathere are large in proportion to their thickness, and are gently curved. Their grinding surface is simple and well adapted to the comminution of leaves and twigs. They are all of them molars (grinding teeth), and there are four on each side of each jaw. They consist of regular foursided prisms, the outer coating being of bony matter, enclosing a thin inner coating of enamel, and a central mass of ivory; while the opposing teeth are so placed in the jaw that the enamel of each cuts into the softer bone and into the central ivory of the corresponding. one, so that a grinding surface is constantly and evenly preserved, and two wedge-shaped cutting edges work into one another, and keep one another sharp.

These teeth were renewed from the root throughout the entire life of the animal, and were gradually pushed forwards as they were needed. They were set very deep in the jaw. It is worthy of notice, that many of these modifications, the narrow palate for instance, the position of the teeth closely set in the jaw, their great length, and the corresponding depth of the jaw, all exhibit a certain amount of resemblance to the structure of corresponding parts of the elephant, although the fundamental structure of the teeth, and the general form of the skull, is at present exclusively restricted to the sloth family.

I shall not dwell long on the description of the vertebral column and the ribs of the Megatherium. The neck is strong, but not remarkably so. It is of moderate length, and differs from that of the three-toed sloth in a point in which this latter quadruped differs from all others, namely, the possession of an additional vertebra of the neck. In this respect, indeed, the two-toed sloth, or unau, (another existing species,) approaches the megatheroid type, but is itself anomalous, exhibiting an increased number of dorsal vertebræ, so that the extinct genus did not agree in this respect with either of the existing sloths inhabiting trees. In the tail, also, the difference is marked not less strongly, for the sloth is unprovided with any such appendage, while it formed a prominent and important organ of support in the Megatherium and other extinct species.

The ribs, both of the Megatherium and the sloth, are broad, and offer a firm support to the body of the animal. Those which are interlocked among each other to form the breast-bone offer an example of a very singular structure, found not in the sloth but in the ant-eaters, and apparently intended to assist these animals when burrowing through the earth. The resisting power and the strength thus afforded to the fore extremities was exceedingly great.

But by far the most remarkable part of the megathere is seen in the posterior portion of the skeleton, commencing with the lumbar vertebræ, and including the bones of the pelvis, the tail, and the hinder extremities.

In all these there may be traced a succession of contrivances strikingly indicative of enormous, un