NOTICE OF THE MEGATHERIUM. 
motion of the head. The roof of the mouth is hollowed into 
a shallow furrow, forming, with a still deeper depression in 
the jaw below, a suitable chamber for a long, cylindrical and 
powerfully muscular tongue; while the sharp truncation of 
the muzzle, the deep excavation of its end, and the foramina 
for the passage of nerves and vessels seem to indicate the 
possession of a short proboscis. The lower jaw is of a very 
singular and extreme type, being nearly as great in vertical 
measure as in length. Much of this depth is due to a great 
downward expansion of the portion which bears the teeth, 
a modification necessitated by the very peculiar manner in 
which these latter are sustained in their growth. The depth 
of the jaw here is no less than nine inches and a half. The 
dental formula of the Megatherium is m. -f 1=18; the teeth 
being all molars, ten above and eight below. They are 
from 8 to 10 inches in length, and between 2 and 3 inches 
flattened prism with square corners, and slightly curved between their two ends. They are 
almost wholly buried in the jaw, with a single root of the same size and form as the crown. 
They repeat in their structure the dental peculiarities of the modern Sloth. A central axis 
of vaso-dentine is inclosed by a wall of unvascular dentine, and this by one of cement, and 
the teeth are so disposed in the two jaws that in the act of mastication, the hard dentine of 
one tooth came in contact with the softer part of its antagonist. So that a series of wedges 
or chisels, locking into each other, were perpetually formed and maintained by the simple 
wear of the teeth themselves. The nutritive fluid circulated through all their substance, and 
Section of Upper Molar Teeth. 
vd. vascular dentine, d. unvascular dentine, c. cement, 
pc. pulp-cavity. 
the growth and renewal of the whole took place in a large pulp-cavity at the base, which ex- 
tended, with slightly diminished size, far up toward the crown of the tooth. This endowment 
