NATURAL HISTORY OF THE PRIMEVAL WORLD. 



Dr. Buckland points out that the sacral bone is 

 united to the pelvis in a very singular manner, evi- 

 dently with the object of securing the greatest possible 

 amount of strength, while its processes indicate that 

 the muscles regulating the movement of the tail were 

 of great power. 



The tail was long, and composed of vertebrae of 

 enormous magnitude ; the body of the largest measur- 

 ing not less than seven inches in diameter, while the 

 distance horizontally between the extremities of the 

 two transverse processes was twenty inches. Include 

 the thickness of the muscles and tendons, and of the 

 shelly integument, and you cannot estimate the dia- 

 meter of the tail at its root at less than two feet ; 

 while its circumference, supposing it to be nearly cir- 

 cular, like the tail of the armadillo, would be about 

 six feet, or twice the size of a well-grown man. These 

 vast dimensions, observes our authority, are not larger, 

 in proportion to the adjacent parts of the body, than 

 those of the armadillo ; and as this animal makes use 

 of its tail as an auxiliary in supporting the weight of 

 its body and armour, we may reasonably infer that the 

 Megatherium employed its huge caudal extremity in a 

 similar manner.* The large inferior spines, or addi- 

 tional chevron bones, attached to the caudal vertebrae, 

 by increasing the strength of the tail, would render 

 it more useful in this important rest. But the tail 

 was also probably employed as a powerful defensive 

 weapon, like that of the crocodiles and pangolins. 



The ribs of the Megatherium are at once thicker, 

 shorter, and more substantial than those of the rhino- 

 ceros or elephant; and in some of them the convex 

 tipper surfaces exhibit a rugose and flattened condi- 

 tion, showing the points where the weight of the bony 

 cuirass chiefly rested. 



The scapula, or shoulder-bone, is unlike that of any 

 other family, except the Sloth, and displays in the 

 acromioii " contrivances for strength, peculiar to itself 

 and them, in its mode of articulation with the collar- 

 bone ; it also exhibits unusual provisions for the support 

 of the most powerful muscles for the movement of 

 the arm." 



The clavicle, or collar-bone, is strong, and incur- 

 vated nearly as in man. From the presence of this 

 bone, which is wanting in the elephant, the rhinoceros, 

 and all the large Kuminantia, we conclude that the 

 fore-leg fulfilled some other function than that of a 

 mere locomotive organ. This clavicle would afford a 

 steady and permanent position to the socket, or glenoid 

 cavity of the scapula, and so permit the animal's fore- 

 leg, like the human arm, to move freely in a rotatory 

 manner. 



In these circumstances we find, says Dr. Buckland, 

 whose admirable description of the Megatherium we 

 have closely followed 1st, That a free rotatory power 

 of the fore-leg was auxiliary to its office as an instru- 

 ment to be continually employed in digging food out 

 of the ground ; 2nd, That this act of perpetual digging 

 in search of stationary objects like roots, needed but 



* The elephant's tail is remarkably light and slender, being 

 chiefly used to brush off insects ; that of the hippopotamus, 

 being intended to act like a rudder when the animal is swim- 

 ming, is only a few inches long, and vertically flattened. 



little locomotive power ; and 3rd, That the compara- 

 tively slight support rendered to the weight of the 

 huge armour-plated body by the fore-leg, was abun- 

 dantly compensated by the extraordinary, the almost 

 gigantic strength, of the haunches and hind legs. 



In the elephant the excessive weight of the animal's 

 head, proboscis, and tusks require a short, thick neck, 

 and a proportionate development and solidity in the 

 fore-legs, which are consequently built up, so to speak, 

 on a stronger and bolder scale than the posterior ex- 

 tremities ; but with the Megatherium we find the relative 

 proportions reversed : a small head is accompanied by 

 a long neck, and the anterior portions of its body are 

 but slightly weighted in comparison with its abdominal 

 and posterior regions. So exquisite is the foresight, 

 so ingenious the contrivance, which we discover mani- 

 fested in the smallest details of animal organization ! 

 Every want is met as it arises; nowhere does any 

 slovenliness or rudeness prevail, but an abundant pro- 

 vision is made for the comfort, well-being, and com- 

 pleteness of every creature. 



To secure strength and facilitate motion for the fore- 

 legs of the Megatherium there exists, then, a peculiar 

 adaptation of the shoulder-blade and collar-bone. But 

 this strength is not merely intended to sustain the 

 weight of the body, nor is this motion designed to be 

 progressive. The humerus articulates with the scapula 

 by a round head, which admits of unrestrained motion 

 in various directions. It is small at its upper and 

 middle part, but at its lower end attains extraordinary 

 breadth, owing to an enormous expansion of the crests 

 which rise from the condyles, to give origin to the 

 muscles for the movement of the fore-foot and toes : 

 just such an expansion, we must observe, as is found 

 in the lower part of the humerus of the ant-eater, 

 which employs its fore-feet in digging up the solid 

 hills of the termite ants. The ulna is singularly broad 

 and powerful at its upper extremity, affording a large 

 space for the origin of the muscles which regulate the 

 movement of the foot. 



The entire fore-foot must have been about thirty- 

 six inches long and upwards of twelve inches wide, 

 forming a most efficient instrument for moving the 

 earth from that depth within which succulent roots 

 are generally most plentiful. This great length of the 

 fore-foot, when resting upon the ground, however 

 inconsistent with rapid progressive motion, must have 

 been of the highest value in enabling one fore-leg, in 

 conjunction with the hind-legs and tail, to support the 

 whole pressure of the Megatherium's body, w'hile the 

 other fore-leg was exclusively employed in the operation 

 of digging up food. 



The fore-foot of the armadillo (Dasypus peba), and 

 of the Chlamyphorus, is similarly adapted for digging 

 purposes ; and in each may be observed an unusual 

 enlargement and elongation of the extreme bones of 

 the toes for the support of long massive claws. Such, 

 too, was the case with the Megatherium ; the bones 

 supporting the claws were composed partly of an axis, 

 or pointed core, which filled the internal cavity of the 

 horny claw, and partly of a bony sheath forming a 

 strong case to receive and support its root. These 

 claws were placed obliquely to the ground, like the 



