NATURAL HISTORY OF THE PRIMEVAL WORLD. 



digging claws of the mole, and thus were rendered by 

 their very position instruments of greater power for 

 the excavation of the soil. 



We must now glance at the posterior extremities 

 of this huge primeval sloth one of the most interest- 

 ing animals of the antediluvian world. The pelvis 

 was remarkably expansive and solid. The enormous 

 bones of the ilium were set nearly at right angles to 

 the spine of the back, and were more than five feet 

 asunder at their outer margin, thus considerably 

 exceeding the dimensions across the haunches of the 

 largest elephant. Such proportions would have been 

 highly inconvenient for any animal of ordinary stature, 

 but were probably we may rather say unquestionably 

 advantageous to the Megatherium, from its habit of 

 standing for considerable periods on three legs only, 

 while the fourth leg was employed as a digging instru- 

 ment, or in loosening the roots and overturning the 

 trees on whose foliage it browsed. 



But not only was the pelvis distinguished by its 

 breadth and weight ; it was also characterized by an 

 unusual arrangement of the acetabulum, or socket, 

 which articulates with the head of the thigh-bones. 

 While in other animals we find this cavity set more or 

 less obliquely outwards, so as to facilitate the movement 

 of the hind leg, in the Megatherium it was set perpen- 

 dicularly downwards, over the head of the thigh-bone 

 (femur'), and unusually near the spine. Thus it obtained 

 increased power of resisting vertical pressure, though 

 its capacity of rapid motion was diminished. 



As another illustration of the enormous size and 

 power of the muscles of its thigh and leg, we may men- 

 tion the fact that the cavity in the sacrum for the 

 passage of the spinal marrow must have been fully an 

 inch in circumference. 



The gigantic breadth of the pelvis and the adjective 

 employed is not an exaggeration is evidence of the 

 extreme size of the abdominal cavity, of the volumi- 

 nousness of the viscera, and consequent adaptation to 

 the digestion of vegetable food. 



Nor were the form and proportions of the thigh-bone 

 less remarkable. It was nearly three times the thick- 

 ness of the femur of the largest elephant. Its breadth 

 is nearly half its entire length, and a neck of singular 

 strength and shortness, but twenty-two inches in cir- 

 cumference, united its head to the body of the bone. 

 Its length is two feet four inches ; 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, owing to this flatness, expanded outwards " to a 

 degree of which nature presents no other example. " 

 These peculiarities, remarks Dr. Buckland, appear to be 

 subservient to a double purpose; 'first, to give extra- 

 ordinary strength by the shortness and solidity of all 

 its proportions, and secondly, to afford compensation 

 by its external flatness for the weakness which must 

 otherwise have resulted from the inward position of 

 these sockets, by which the femur articulates with the 

 pelvis. 



Not less ingeniously was contrived the articulation of 

 the leg with the hind foot, so as to support the enor- 

 mous downward pressure of the bulky body. The great 

 bone of the instep was nine inches broad and nine inches 



high, and rested upon a heel-bone of the extraordinary 

 length of seventeen, and the not less extraordinary 

 circumference of twenty-eight inches. 



It will readily be understood how solid a support 

 must have been afforded by this colossal bone to that 

 continuous accumulation of weight which we have 

 observed in the pelvis, thigh, and leg. The heel-bone, 

 iu fact, occupied nearly one-half of the entire length of 

 the hind foot. The bones of the toes were all short, 

 excepting the extreme joint, which supported the enor- 

 mous claw ; but they were longer than the largest of 

 those in the fore-foot, measuring thirteen inches in cir- 

 cumference, and having within its sheath a core, two 

 inches long, for the support of the claw already men- 

 tioned, whose chief use perhaps was to keep the hind 

 foot firmly planted upon the ground. 



" Feet and legs thus heavily constructed," says Dr. 

 Buckland, " must have been very inefficient organs of 

 rapid locomotion, and may consequently seem imper- 

 fect, 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 anchor-smith, 

 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." 



Our final view of the structure of the Megatherium 

 will be devoted to its bony armour, the characteristic 

 in which it approaches most nearly to the Armadillo 

 and Chlatnyphorus. There is reason to belie've that its 

 hide was covered with a complete coat of osseous mail, 

 which varied from three-fourths of an inch to an inch 

 and a half in thickness, and resembled the mailed 

 coverings of those living denizens of tropical America. 

 And notwithstanding the great weight of so remarkable 

 "a suit of armour," we cannot pronounce it inconsistent 

 with the general structure of the animal. The huge 

 hind legs and colossal tail of the Megatherium were well 

 able to sustain it ; and the strength of the loins and ribs, 

 greatly exceeding that of the elephant, seems to have 

 been designed for carrying the ponderous cuirass which 

 protected its body. 



But what was the use of this cuirass? What purpose 

 did it serve? It was probably defensive, protecting 

 the animal, not only against the tusks and claws of 

 the voracious quadrupeds which then existed, but also 

 against the legions of insects engendered by a close and 

 sultry climate, to whose attacks an animal that obtained 

 its food by digging beneath a burning sun would be 

 constantly exposed. We may also infer that it was of 

 advantage in defending the back and upper parts of the 

 body, not only against sun, and rain, and insects, but 

 against the accumulations of sand and dust that would 

 otherwise have maintained a constant state of irritability, 

 and resulted iu prolonged disease. 



Similar uses seem 'to be served by the bony covering 

 of the Armadillo and Chlamyphorus, which obtain their 



