those of a Sloth. The long and broad bone, (b,) descending the cheek from the zygomatic arch, connects it more nearly with the Ai than with any other animal: this extraordinary bone must have been auxiliary to the power of muscles, acting with more than usual advantage, in giving motion to the lower jaw (d.)
The anterior part of the muzzle (c) is so strong and substantial, and so perforated with holes for the passage of nerves and vessels, that we may be sure it supported some organ of considerable size: a long trunk was needless to an animal possessing so long a neck; the organ was probably a snout, something like that of the Tapir, sufficiently elongated to gather up roots from the ground. The septum of the nostrils also being strong and bony, gives further indication of the presence of a powerful organ appended to the nose; such an apparatus would have afforded compensation for the absence of incisor teeth and tusks. Having no incisors, the Megatherium could not have lived on grass. The structure of the molar teeth (Pl. 5, Fig. 6—11, and Pl. 6, No. 1,) shows that it was not carnivorous.
The composition of a single molar tooth resembles that of one, of the many denticules, that are united, in the compound molar of the Elephant; and affords an admirable exemplification of the method employed by Nature, whereby three substances, of unequal density, viz. ivory, enamel, and crusta petrosa, or cœmentum, are united in the construction of the teeth of graminivorous animals. The teeth are about seven inches long, and nearly of a prismatic form (Pl. 5, Fig. 7. 8.) The grinding surfaces (Pl. 5. Fig. 9. a. b. c. and Pl. 6, Z. a. b. c.) exhibit a peculiar and beautiful contrivance for maintaining two cutting wedge-shaped salient edges, in good working condition during the whole existence of the tooth; being, as I before stated, a modification of the contrivance employed in the molars of the Elephant, and other herbivore. The same principle is applied by tool-makers for the purpose of maintaining a sharp edge in axes, scythes, bill-hooks,
