42 



NATURAL HISTORY OF THE PRIMEVAL WORLD. 



a peculiarity connecting the Megatherium with the 

 Ai ; this extraordinary bone assisted a powerful set of 

 muscles in giving motion to the lower jaw. The 

 anterior part of the muzzle," according to Dr. Buck- 

 land, of whose admirable description we are largely 

 availing ourselves, "is so strong and substantial, and 

 so perforated with holes for the passage of nerves and 

 vessels, that we may be assured it supported some 



Megatherium restored. 



organ of considerable size. As a long trunk was not 

 needed by an animal with so long a neck, this organ 

 was probably a snout, something like that of the tapir, 

 of sufficient length to gather up roots from the ground. 

 The partition of the nostrils being also strong and bony, 

 furnishes an additional argument for the presence of 

 a powerful organ appended to the nose ; an apparatus 

 which would have sufficiently compensated for the 

 absence of incisor teeth and tusks. Having no incisors, 

 the Megatherium could not have lived upon grass, while 

 the structure of its molar teeth proves that it was not 

 carnivorous. 



"The" composition of a single molar tooth resem- 

 bles that of one of the many denticules that are united 

 in the compound molar of the elephant; and affords 

 an excellent exemplification of the method employed 

 by Nature, whereby three substances of unequal density, 

 viz., ivory, enamel, and ci~usta petrosa, or ccementum, 

 are united in the construction of the teeth of gramini- 

 vorous animals The teeth are about seven inches 

 long, and nearly of a prismatic form. The grinding 

 surfaces exhibit a peculiar and beautiful contrivance 

 for maintaining ten cutting, wedge-shaped, salient edges 

 in good working condition during the whole existence 

 of the tooth ; being, as before stated, a modification 

 of the contrivance employed in the molars of the 



elephant and other Herbivora. The same principle is 

 applied by tool-makers for the purpose of maintaining 

 a sharp edge in axes, scythes, bill-hooks. An axe, or 

 bill-hook, is not made entirely of steel, but of one thin 

 steel plate, inserted between two plates of softer iron, 

 and so inclosed that the steel projects beyond the 

 iron, along the entire line of the cutting edge of the 

 instrument. A double advantage results from this 

 contrivance ; first, the instru- 

 ment is less liable to fracture 

 than if it were entirely made 

 of the more brittle material of 

 steel, and secondly, the cutting 

 edge is more easily kept sharp 

 by grinding down a portion of 

 exterior soft iron, than if the 

 entire mass were of hard steel. 

 By a similar contrivance, two 

 cutting edges are produced on 

 the crown of the molar teeth 

 of the Megatherium." 



Thus the process of mastica- 

 tion formed and maintained in 

 order a series of wedges, locking 

 into each other like the alter- 

 nate ridges on the rollers of a 

 crushing-mill; and the mouth 

 of the Megatherium was con- 

 verted, in effect, into an engine 

 of prodigious power, in which 

 the grinding surfaces of sixteen 

 molar teeth composed double 

 that number of wedges; each 

 tooth was from seven to nine 

 inches long, and for the greater 

 part of its length was firmly 

 embedded in a very deep socket. 

 As the surfaces of these teeth would necessarily 

 wear away with great rapidity, the loss incessantly 

 occurring at the crown was constantly supplied by the 

 addition of new matter at the root, which, for this pur- 

 pose, remained hollow, and filled with pulp throughout 

 the animal's life. Thus, this exquisite mechanical 

 apparatus maintained itself in perfect order by the very 

 act of performing its own work. 



In proportion to the rest of the head the lower 

 jaw is exceedingly large and weighty, having been so 

 constructed for the purpose of affording deep sockets 

 for the solid fixture and incessant growth of the long 

 vertical molar teeth. And as it became necessary to 

 provide a support for a jaw of this unusual bulk, the 

 "process" descending from the so-called zygomatic 

 arch in the Megatherium, as in all the sloths, is 

 fashioned with unusual strength and rigidity. 



The vertebrae of the neck, compared with those 

 towards the opposite extremity of the body, are really 

 small, but yet of sufficient size for the movements of 

 a head which is of no excessive weight, and without 

 tusks. The dorsal portion of the vertebral column is 

 of moderate size, but the vertebrae of the loins enlarge, 

 so as to correspond with the huge pelvis and colossal 

 hind-legs. The summits of the spiuous processes are 

 flattened like those in the armadillo. 



