are not larger in proportion to the adjacent parts of the body, than those of the tail of the Armadillo, and as this animal applies its tail, to aid in supporting the weight of its body and armour, it is probable that the Megatherium made a similar use of the same organ.* To the caudal vertebræ were attached also large inferior spines, or additional Chevron bones, which must have added to the strength of the tail, in assisting to support the body. The tail also probably served for a formidable instrument of defence, as in the Pangolens and Crocodiles. In 1822, Sellow saw portions of armour that had covered a tail, found near Monto Video.

The ribs are more substantial, and much thicker, and shorter, than those of the Elephant or Rhinoceros; and the upper convex surfaces of some of them exhibit a rugous and flattened condition of that part, on which the weight of a bony cuirass would most immediately have rested.

Anterior Extremity.

The scapula or shoulder blade, (Pl. 5, Fig. 1, f,) resembles that of no other family except the Sloths, and exhibits in the Acromion (g,) contrivances for strength, peculiar to itself and them, in its mode of articulation with the collar bone (h;) it exhibits also unusual provisions for the support of the most powerful muscles for the movement of the arm.

The clavicle or collar bone (h) is strong, and curved nearly as in the human subject; the presence of this bone in the Megatherium, whilst it is wanting in the Elephant, Rhinoceros, and all the large ruminating animals, shows that the fore-leg discharged some other office, than that of an

• The tail of the Elephant is remarkably light and slender, with a tuft of coarse hair at its extremity, to brush off flies; that of the Hippopotamus is a few inches only in length, and flattened vertically, to act as a small rudder in swimming.

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organ of locomotion. This clavicle would give a steady and fixed position to the socket, or glenoid cavity of the scapula, admitting of rotatory motion in the fore-leg, analogous to that of the human arm. There is in these circumstances a triple accommodation to the form and habits of the Megatherium; 10. a free rotatory power of the arm was auxiliary to its office, as an instrument to be employed continually in digging food out of the ground; 2°. this act of perpetual digging in search of stationary objects like roots, required but little locomotive power; 3°. the comparatively small support afforded to the weight of the body by the fore-leg, was compensated by the extraordinary and colossal strength of the haunches and hind legs. In the Elephant, the great weight of the head and tusks require shortness of neck, and unusual enlargement and strength in the fore-legs; hence, the anterior parts of this animal are much stronger and larger than its hinder parts. In the case of the Megatherium, the relative proportions are reversed; the head is comparatively small, the neck is long, and the anterior part of the body but slightly loaded in comparison with its abdominal and posterior regions. In the shoulder blade and collar bone there is great provision to give strength and motion to the fore-legs; but this motion is not progressive, nor is the strength calculated merely to support the weight of the body. The humerus, (k) articulates with the scapula by a round head, admitting of free motion in various directions, and is small at its upper and middle part, but at its lower end attains extraordinary breadth, in consequence of an enormous expansion of the crests, which rise from the condyles, to give origin to muscles for the movement of the forefoot and toes. The ulna (1) is extremely broad and powerful at its upper extremity, affording large space for the

* There is a similar expansion of the lower part of the Humerus in the Ant-eater, which employs its fore-feet in digging up the solid hills of the Termite Ants.

origin of muscles, concerned in the movements of the foot. The radius (m) revolves freely on the ulna, as in the Sloths and Ant-eaters, both of which make much use of the foreleg, though for different purposes; it has a cavity at its upper end, which turns upon a spherical portion of the lower part of the humerus, and a large apophysis (n,) projecting from its longitudinal crest, indicates great power in the muscles that gave rotatory motion.

The entire fore-foot must have been about a yard in length, and more than twelve inches wide; forming a most efficient instrument for moving the earth, from that depth within which succulent roots are usually most abundant. This great length of the fore-foot, when resting upon the ground, though unfavourable to progressive motion, must have enabled one fore-leg, when acting in conjunction with the two hind-legs and tail, to support the entire weight of the body; leaving the other fore-leg at liberty to be employed exclusively in the operation of digging food.*

The toes of the fore-foot are terminated by large and powerful claws of great length; the bones, supporting these claws, are composed partly of an axis, or pointed core, (o,) which filled the internal cavity of the horny claw; and partly of a bony sheath, that formed a strong case to receive and support its base. These claws were set obliquely to the ground, like the digging claws of the Mole, a position which made them instruments of greater power for the purpose of excavation.

* At Pl. 5, beneath Fig. 1, are represented the fore-foot of an Armadillo (Daspyus Peba,) and the fore-foot of the Chlamyphorus, each adapted, like that of the Megatherium, to form an instrument of peculiar power for the purpose of digging; and each presenting an extraordinary enlargement and elongation of the extreme bones of the toes, for the support of long and massive claws. At Pl. 5, Figs. 18, 19, the anterior parts of these animals are represented, and show how large a proportion the claws bear to the other parts of the body.

Posterior Extremities.

The pelvis of the Megatherium (Pl. 5, Fig. 2. p.) is of vast solidity and expanse; and the enormous bones of the ileum (r) are set nearly at right angles to the spine of the back, and at their outer margin, or crest, are more than five feet asunder, very much exceeding the diameter across the haunches of the largest elephant: the crest of the ileum, (s,) is much flattened, as if by the pressure of the armour. This enormous size of the pelvis would be disproportionate and inconvenient to an animal of ordinary stature and functions; but was probably attended with much advantage to the Megatherium, in relation to its habit of standing great part of its time on three legs, whilst the fourth was occupied in digging.

The pelvis being thus, unusually wide and heavy, presents a farther deviation from other animals, as to the place and direction of the acetabulum, or socket which articulates with the head of the thigh-bone (u.) This cavity, in other animals, is usually set more or less obliquely outwards, and by this obliquity facilitates the movement of the hind-leg; but in the Megatherium it is set perpendicularly downwards, over the head of the femur, and is also nearer than usual to the spine; deriving from this position increase of strength for supporting vertical pressure, but attended with a diminished capability of rapid motion.*

* There is also a farther peculiarity for the increase of strength in the manner in which that part, which, in most other animals, is an open space, called the ischiatic notch (Pl. 5, Fig. 2 c.) is nearly closed with solid bone by the union of the spines of the ischia with the elongated transverse processes of the sacral vertebræ, (a.)

Farther evidence of the enormous size and power in the muscles of the thigh and leg is afforded by the magnitude of the cavity in the sacrum, (Pl. 5. d,) for the passage of the spinal marrow: this cavity being about four inches in diameter, the spinal marrow must have been a foot in circumfeThe extraordinary magnitude also of the nerves which proceeded from it to supply the leg, is indicated by the prodigious size of the sacral foramina.

rence.

From the enormous width of the pelvis, it follows also that the abdominal cavity was extremely large, and the viscera voluminous, and adapted to the digestion of vegetable food.

The form and proportions of the thigh-bone, (v) are not less extraordinary than those of the pelvis, being nearly three times the thickness of the femur of the largest Elephant. Its breadth is nearly half its entire length, and its head is united to the body of the bone by a neck of unusual shortness and strength, twenty-two inches in circumference. Its length is two feet four inches, and its circumference at the smallest part, two feet two inches; and at the largest part, three feet two inches. Its body is also flattened; and by means of this flatness, expanded outwards to a degree of which Nature presents no other example. These peculiarities in the femur appear to be subservient to a double purpose: first, to give extraordinary strength by the shortness and solidity of all its proportions; and secondly, to afford compensation by its flatness outwards; for the debility which would otherwise have followed from the inward position of the sockets, (t,) by which the femur, (u,) articulates with the pelvis.

The two bones of the leg (x, y,) are also extremely short, and on a scale of solidity and strength, commensurate with that of the femur that rests upon them. This strength is much increased by their being united at both extremities; a union which is said by Cuvier to occur in no other animals except the Armadillo and Chlamyphorus; both of which are continually occupied in digging for their food.

The articulation of the leg with the hind-foot is admirably contrived for supporting the enormous pressure of downward weight; the astragalus (z,) or great bone of the instep, being nine inches broad and nine inches high, is in due proportion to the lower extremity of the tibia, or leg-bone, with which it articulates; and rests upon a heel-bone, of the extraordinary length of seventeen inches, with a circumference of