twenty-eight inches. This enormous bone, pressing on the ground, gives a firm bearing and solid support to the continuous accumulation of weight, which we have been tracing down from the pelvis through the thigh and leg: in fact the heel-bone occupies nearly one-half of the entire length of the hind-foot; the bones of the toes are all short, excepting the extreme joint, which forms an enormous claw-bone; larger than the largest of those in the fore-foot, measuring thirteen inches in circumference, and having within its sheath a core, ten inches long, for the support of the horny claw with which it was invested. The chief use of this large claw was probably to keep the hind-foot fixed steadily upon the ground.*

Feet and legs thus heavily constructed, must have been very inefficient organs of rapid locomotion, and may consequently seem imperfect, if considered in relation to the ordinary functions of other quadrupeds; but, viewed as instruments adapted for supporting an almost stationary creature, of unusual weight, they claim our admiration equally with every other piece of animal mechanism, when its end and uses are understood. The perfection of any instrument can only be appreciated by looking to the work it is intended to perform. The hammer and anvil of an anchorsmith, though massive, are neither clumsy nor imperfect; but bear the same proportionate relation to the work in which they are employed, as the light and fine tools of the watchmaker bear to the more delicate wheels of his chronometer.

Bony Armour.

Another remarkable character of the Megatherium, in which it approaches most nearly to the Armadillo, and

*It is probable that the large thick claw, Pl. 5 5', was placed on the second toe of the hind-foot. Its size approaches nearly to that of the first toe of this foot, and both of these differ materially in form and propor

Chlamyphorus, consists, in its hide having probably been covered with a bony coat of armour; varying from threefourths of an inch, to an inch and a half in thickness, and resembling the armour which covers these living inhabitants, of the same warm and sandy regions of South America. Fragments of this armour are represented at Pl. 5, Figs. 12, 13.*

A covering of such enormous weight, would have been consistent with the general structure of the Megatherium; its columnar hind-legs and colossal tail, were calculated to give it due support; and the strength of the loins and ribs, being very much greater than in the Elephant, seems to have been necessary for carrying so ponderous a cuirass as that which we suppose to have covered the body.t

tions, from the three more elongated and flatter claw-bones of the fore-foot, the oblique form of which is peculiarly adapted for digging.

*The resemblance between some parts of this fossil armour, and of the armour of an Armadillo, (Dasypus Peba) is extended even to the detail of the patterns of the tuberculated compartments into which they are divided, see Pl. 5, Figs. 12, 14. The increase of size in the entire shield is in both cases provided for, by causing the centre of every plate to form a centre of growth, around which the margin receives continual additions, as the increasing bulk of the body requires an increase in the dimensions of the bony case, by which it is invested. Figs. 15, 16, 17, represent portions of the armour of the head, body, and tail piece of the Chlamyphorus. Figs. 18, 19, represent the manner in which the armour is disposed over the head and anterior part of the body of the Chlamyphorus, and Dasypus Peba. The body of the Megatherium, when covered with its corresponding coat of armour, must in some degree have resembled a tilted wagon.

In the transactions of the Academy of Berlin, 1830, Professor Weiss has published an account of some bones of the Megatherium, discovered near Monte Video, accompanied by several fragments of bony armour. Much of this armour he refers without doubt to the Megatherium; other portions of it, and also many bones from the same district, he assigns to other animals. A similar admixture of bones and armour, derived from more than one species of animal, bearing a bony cuirass, is found in the collection. made at several and distant points of the country above Buenos Ayres, by

It remains to consider, of what use this cuirass could have been to the gigantic animal on which it probably was placed. As the locomotive organs of the Megatherium indicate very slow power of progression, the weight of a cuirass would have afforded little impediment to such tardy movements; its use was probably defensive, not only against the tusks and claws of beasts of prey, but also, against the myriads of insects, that usually swarm in such climates as those wherein its bones are found; and to which an animal that obtained its food by digging beneath a broiling sun, would be in a peculiar degree exposed. We may also conjecture it to have had a farther use in the protection afforded by it to the back, and upper parts of the body; not only against the sun and rain, but against the accumulations of sand and dust, that might otherwise have produced irritation and disease.*

Mr. Parish. Although no armour was found with the fragments of the large skeleton, in the bed of the Salado, the rough broad flattened surface of a part of the crest of the ileum of this skeleton, (see Pl. 5, Fig. 2. r, s,) and the broad condition of the summit of the spinous processes of many vertebræ, and also of the superior convex portion of certain ribs on which the armour would rest, afford evidence of pressure, similar to that we find on the ana logous parts of the skeleton of the Armadillo, from which we might have inferred that the Megatherium also was covered with heavy armour, even had no such armour been discovered. near bones of this animal in other parts of the same level district of Paraguay. In all these flattened bones the effects of pressure are confined to those parts of the skeleton, on which the armour would rest, and are such as occur in a remarkable degree in the Armadillo.

* To animals that dig only occasionally, like Badgers, Foxes, and Rabbits, to form a habitation beneath the ground, but seek their food upon the surface, a defence of this kind would not only have been unnecessary but inconvenient.

The Armadillo and Chlamyphorus are the only known animals that have a coat of armour composed of thick plates of bone, like that of the Megatherium. As this peculiar covering is confined to these quadrupeds, we can hardly imagine its use to be solely for protection against other beasts and insects; but as the Armadillo obtains its food by digging in.

Conclusion.

We have now examined in detail the skeleton of an extinct quadruped of enormous magnitude; every bone of which presents peculiarities, that at first sight appear imperfectly contrived, but which become intelligible when viewed in their relations to one another, and to the functions of the animal in which they occur.

The size of the Megatherium exceeds that of the existing Edentata, to which it is most nearly allied, in a greater degree than any other fossil animal exceeds its nearest living congeners. With the head and shoulders of a Sloth, it combined in its legs and feet, an admixture of the characters of the Ant-eater, the Armadillo, and the Chlamyphorus ; it probably also still farther resembled the Armadillo and Chlamyphorus, in being cased with a bony coat of armour. Its haunches were more than five feet wide, and its body twelve feet long and eight feet high; its feet were a yard in length, and terminated by most gigantic claws; its tail was probably clad in armour, and much larger than the tail of any other beast, among extinct or living terrestrial Mammalia. Thus heavily constructed, and ponderously accoutred, it could neither run, nor leap, nor climb, nor burrow under the ground, and in all its movements must have been necessarily slow; but what need of rapid locomotion to an animal, whose occupation of digging roots for food was almost stationary? and what need of speed for flight from foes, to a creature whose giant carcass was encased in an inpenetrable cuirass, and who by a single pat of his paw,

the same dry and sandy plains, which were once inhabited by the Megatherium, and the Chlamy phorus lives almost entirely in burrows beneath the surface of the same sandy regions; they both probably receive from their cuirass the same protection to the upper parts of their bodies from sand and dust, which we suppose to have been afforded by its cuirass to the Megatherium. The Pangolins are covered with a different kind of armour, composed of horny moveable scales, in which there is no bony

matter.

or lash of his tail, could in an instant have demolished the Couguar or the Crocodile? Secure within the panoply of his bony armour, where was the enemy that would dare encounter this Leviathan of the Pampas? or, in what more powerful creature can we find the cause that has effected the extirpation of his race?

His entire frame was an apparatus of colossal mechanism, adapted exactly to the work it had to do; strong and ponderous, in proportion as this work was heavy, and calculated to be the vehicle of life and enjoyment to a gigantic race of quadrupeds; which, though they have ceased to be counted among the living inhabitants of our planet, have, in their fossil bones, left behind them imperishable monuments of the consummate skill with which they were constructed. Each limb, and fragment of a limb, forming co-ordinate parts of a well-adjusted and perfect whole; and through all their deviations from the form and proportion of the limbs of other quadrupeds, affording fresh proofs of the infinitely varied, and inexhaustible contrivances of Creative Wisdom.

SECTION III.

FOSSIL SAURIANS..

In those distant ages that elapsed during the formation of strata of the secondary series, so large a field was occupied by reptiles, referable to the order of Saurians, that it becomes an important part of our inquiry to examine the history and organization of these curious relics of ancient creations, which are known to us only in a fossil state. A task like this may appear quite hopeless to persons unaccustomed to the investigation of subjects of such remote antiquity; yet Geology, as now pursued, with the aid of comparative anatomy, supplies abundant evidence of the struc