seen in the slope of the back part of the head, which is characteristic of the dinothere, and common to the Cetacea and some of the rodents. A very limited capacity is thus indicated, and the indication is strengthened by the exceedingly small space that there is for the brain.

The teeth of the Toxodon are very interesting. All the grinding teeth are long and curved; but unlike the case of the guinea-pig, whose teeth, also curved, are directed outwards, the curve is here such, that each two corresponding teeth of the upper jaw bend over to meet each other in the palate and form an arch capable of overcoming immense resistance to pressure.

The two large incisive teeth, in like manner, bend backwards in their sockets, and extend in an arched form as far as the grinding teeth. The whole of the inside of the upper jaw is thus a vaulted and groined roof of the strongest possible construction; and as the teeth continued to grow and to be pushed forward during the whole life of the animal, there was a constant and continual compensation to meet the effect of the wearing away of the crown of the tooth against opposing teeth of corresponding structure in the lower jaw. The enamel of the teeth is not repeated in distinct folds as in the herbivorous animals of the present day, but the powers of perpetual renovation would amply compensate for this defective quantity of enamel, and enable the animal to grind down vegetable food of the toughest kind, without danger of ultimately wearing away the grinding surface. It is evident, however, from the nature of the attachment of the lower jaw, that the motion

of the jaw in the process of mastication was not the same as in the rodents, but admitted of considerable lateral motion and great pressure, assisting in the trituration of the food. There was also a powerful muscular apparatus enabling the jaws to be worked sideways; and it appears from the bones of the face, that those muscles, by which the incisive teeth. and the extremities of the jaws were worked, and which form the lips, were also exceedingly large and strong; these fore-teeth being probably used (like the corresponding teeth of the hippopotamus) to divide or tear up by the roots the aquatic plants growing on the banks of the streams which the Toxodon may have frequented. It also appears that the lips of this singular animal were endowed with great sensibility, large nerves having been supplied for such purpose. The expanded muzzle seems even to have been furnished with whiskers.

The extremities of the Toxodon are not at all known, nor can it be distinctly determined whether they were such as to enable the animal to move about on land, or whether, like the dugong and other herbivorous cetaceans, it remained permanently in the water. It is considered unlikely, however, that the latter was the case, although there are not wanting some curious points of structure indicative of its aquatic habits. The affinities exhibited both to the rodent and cetacean orders are very remarkable, this pachydermatous animal, of gigantic proportions, being characterised by teeth which closely resemble those of the gnawing tribes, while the structure of some bones of the skull approaches in many respects to that of the whales.

The knowledge that we possess of the Toxodon is derived entirely from a consideration of some of the bones of the head. We have next to deduce the habits and instincts of another extinct genus, of which nothing is known but a few bones of the trunk and the extremities, without a fragment of a tooth or of the skull to serve as a guide in the investigation. It is the triumph of comparative anatomy that such an investigation is possible; and few things in scientific induction are more beautiful than the nature of the arguments by which, in these cases, the results of the investigation of each bone and fragment of a bone are shewn to bear upon and explain one another.

The animal I have now to describe is called Macrauchenia,* from the great length and magnitude of its neck, which was very nearly as long as that of the giraffe. Its analogies have been beautifully and admirably worked out by Professor Owen, and he has referred it with great certainty and confidence to the order Pachydermata. It belongs also to that group (containing the rhinoceros and palæotherium) of which the various species are not provided with a proboscis, and have only three toes on the fore-foot. The fore and hind feet of the Macrauchenia were of equal size. The body was nearly as large and massive as that of the rhinoceros, and the length of the legs very much greater. The long neck was not carried gracefully as in the giraffe, but in a stiff and upright position like that of the llama; and the whole appearance of the animal must have been heavy, awkward, and ungainly. It is interesting to find

* Marpos (makros), long; avxnv (auchen), the neck.

that its nearest analogies are with the extinct genus Palæotherium, but it also indicates a very beautiful transition from the pachyderms to the ruminants, through the singular group of which the camels and the llama are the existing representatives. A true anoplotheroid animal has recently been added to the list of South American pachyderms.

We now come to the consideration of those animals more especially characteristic of the later tertiary period on the continent of South America,—a group of animals perhaps the most remarkable of any that has yet been determined, and one which exhibits a perfect and beautiful adaptation of closely analogous structure in the case of species varying in bulk almost as much as it is possible for those of analogous structure to do. All the rest of the quadrupeds that I shall have to describe belong to the same natural order, which includes, with few exceptions, the great majority of those fossils hitherto obtained from South America. The order, as I have already stated, is called Edentata, and is now characterised by the sloth, the armadillo, and the ant-eater. Of the existing species of these animals, the largest is the great ant-eater, which equals in length a Newfoundland dog of the others, the gigantic armadillo attains about two-thirds of that bulk; and the sloth never exceeds two feet in the length of the body, although its fore extremities are disproportionately long. At the time immediately preceding the last change that took place upon the earth, South America was, however, inhabited by numerous animals of this order, some of them rivalling in bulk the largest pachyderms, and others quite as remarkable for their structure, their

appearance, and their habits, as for their strange analogies with the sloth and the armadillo.

The sloth is well known and exceedingly common in some of the forests of South America.

It has

very long fore-legs, so constructed as to support the animal when hanging on the under side of the branch of a tree, and in this position it usually rests. It never willingly descends to the earth, where the peculiar form of its limbs prevents it from advancing without great and painful efforts; but when on a tree it moves rapidly and with ease, passing from one branch to another, and getting from tree to tree by the help of the numerous parasitical plants which form a net-work uniting the upper branches of the most lofty trees of the forest. The animal is not provided with a tail, and the want of such an appendage is not felt, the bones of the extremities and the powerful toes forming an ample support for the creature whether moving or resting suspended from a branch.

It is curious and very interesting to see all the most marked peculiarities of the skeleton, so far as relates to the essential structure of this animal, transferred, on a gigantic scale, to some extinct species, while at the same time the modifications observable in the shortening and strengthening of the legs, and the addition of a powerful tail, are quite enough to convince the physiological naturalist that the actual habits must have differed in spite of much essential and important resemblance.

One of these huge monsters has been well named Megatherium; and nearly every bone of its enor

*

Meya (mega), great; Onpiov (therion), a beast.