138 FOSSIL MAMMALIA. 
rivers. To an animal of such habits, the weight 
of the tusks sustained in water would have been 
no source of inconvenience ; and, if we suppose 
them to have been employed, as instruments for 
raking and grubbing up by the roots large 
aquatic vegetables from the bottom, they would, 
under such service, combine the mechanical 
powers of the pick-axe with those of the horse- 
harrow of modern husbandry. The weight of 
the head, placed above these downward tusks, 
would add to their efficiency for the service here 
supposed, as the power of the harrow is increased 
by being loaded with weights. 
The tusks of the Dinotherium may also have 
been applied with mechanical advantage to hook 
on the head of the animal to the bank, with the 
nostrils sustained above the water, so as to 
breathe securely during sleep, whilst the body 
remained floating, at perfect ease, beneath 
the surface : the animal might thus repose, 
moored to the margin of a lake or river, 
without the slightest muscular exertion, the 
weight of the head and body tending to fix and 
keep the tusks fast anchored in the substance of 
the bank ; as the weight of the body of a sleep- 
ing bird keeps the claws clasped firmly around 
its perch. These tusks might have been further 
used, like those in the upper jaw of the Wal- 
rus, to assist in dragging the body out of the 
water ; and also as formidable instruments of 
defence. 
