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ANATOMY AND PHYSIOLOGY 
is most probable, since tbe depth of the jaw is also in- 
creased, so that the teeth appear to sink deeper and deeper 
in the jaw. This formation is readily discovered in jaws 
not full grown, for the teeth increase in number as the 
jaw r lengthens, as in other animals. The posterior part 
of the jaw becoming longer, the number of teeth in that 
part increases, the sockets becoming shallower and shal- 
lower, and at last being only a slight depression. It 
would appear that they do not shed their teeth, nor have 
they new ones formed similar to the old, as is the case 
with most quadrupeds, and also with the alligator. I 
have never been able to detect young teeth under the 
roots of the old ones ; and indeed, the situation in which 
they are first formed makes it in some degree impossible, 
if the young teeth follow the same rule in growing with 
the original ones, as they probably do in most animals. 
If it is true that the whale tribe do not shed their 
teeth, in what way are they supplied with new ones, cor- 
responding in size with the increased size of the jaw? 
It would appear that the jaw, as it increases posteriorly, 
decays at the symphysis ; and while the growth is going 
on there is a constant succession of new teeth, by which 
means the new formed teeth are proportioned to the jaw. 
The same mode of growth is evident in the elephant, 
and in some degree in many fish, but in these last the 
absorption of the jaw is from the whole of the outside 
along where the teeth are placed. The depth of the 
alveoli seem to prove this, being shallow at the back part 
of the jaw, and becoming deeper towards the middle, 
where they are deepest, the teeth there having come to 
