10 
NOTICE OF THE MEGATHERIUM. 
and of triangular form. The vigor of the muscles attached to it is manifested by the spines 
and ridges on its outer surface. The confluence of the acromium with the coracoid process is 
a peculiarity which the Megatherium shares with the modern Sloths. The glenoid cavity is 
elliptical, and its greatest diameter is six and a half inches. The clavicle is 15 inches in length? 
and much resembles that of man in shape* The humerus and the fore-arm by the devel- 
opment of their inequalities bespeak the great volume and force of the muscular masses 
which surrounded them. The distal end of the humerus is so flattened vertically, and 
extended at its sides as to be IB inches in width ; that of the Rhinoceros being only one-third 
as large, and the Elphant’s only one-fourth. The head of the radius has a shallow, concave, 
articular surface, which allows quite as much rotary movement as in the arm of man. The ulna is 
peculiar by reason of the great expansion of its proximal end in connexion with its long and 
slender shaft. The forefoot consists of 7 carpal bones, 5. metacarpal, and 10 phalanges. The 
2d, 3d and 4th digits were furnished with claws. The place of the thumb was held by a 
stunted metacarpal. The entire length of the fore-leg, with the foot, is seven feet and foui 
inches, and its proportions are in harmony with the rest of the animal structure. 
The Posterior Extremities are shorter than the anterior. The pelvis, which forms the 
most striking feature in the skeleton, is the largest single bone of any land animal either living, 
or extinct. Its extreme breadth is upwards of five feet, being sixteen inches broader than the 
pelvis of the Asiatic Elephant. Viewed in front, the two iliac bones resemble a pair of out- 
stretched wings, the concave surfaces facing the head. The two sides of the pubis unite in a 
long, slender, wedge-shaped bone, reaching downwards and forwards at right angles to the trans- 
verse axis of the superior ilia and ischia. The socket for the head of the femur is a well-defined 
oval cavity, the concave surface of which measures nearly forty-four square inches ; the atmo- 
spheric pressure upon the hip-joint of the animal is 660 pounds.f The thigh-bones of the 
Mastodon and Elephant appear weak and slender when compared with the massive femur of 
the Megatherium. It is about two feet four inches long by three feet two inches in circum- 
ference at the largest part, and its surface is roughened by two rugged trochanters. It is 
much flattened before and behind, and the anterior surface of the shaft is so hollowed out 
as to form quite an arc with a line drawn between the two extremities of the bone. The distal 
extremity joins firmly, with two articular surfaces, to the upper end of the tibia. The tibia 
and fibula are anchylosed together at both extremities, by which their strength is much 
increased. Altogether the hind legs appear more like columns for support than organs of 
locomotion. Their articulation with the feet is admirably contrived for supporting the enor- 
mous pressure of downward weight, which is transmitted to the middle of the pedal arch. 
The astragalus, or great bone of the instep, is 9 inches broad, and the same_m height. Its 
articular surface is so placed upon the inner side, that the foot, when joined to the leg, is 
* The Megatherium had the largest clavicle of-any animal of geological times, as has man among all ani- 
mals of the present creation. 
f How does the anatomy of this huge beast contrast with that of some other animals which, in point of 
size, hold their place at the other end of the long series of Mammalian forms. In the Megatherium the cavity 
of the acetabulum is eight inches in diameter ; in the pigmy Shrew Mouse — Sorex araneus — it is about one 
half of a line across, or only about one two hundredth of the former dimension ! 
