StruSlure and 0 economy of Whales. 399 
fattened in the gum, the other projecting : they are, however, 
not all exaCUy of this fhape. In fome fpeeies of Porpoife the 
fang is flattened, and thin at its extremity ; in the Spermaceti 
Whale the body of the tooth is a little curved towards the 
back part of the mouth ; this is alfo the cafe in fome others. 
The teeth are compofed of animal fubftance and earth, limjlar 
to the bonv part of the teeth in quadrupeds. The upper teeth are 
commonly worn down upon the infide, the lower on the out- 
lkle ; this arifes from the upper jaw being in general the larger!. 
The fituation of the teeth, when firft formed, and their progrefs 
afterwards, as far as I have been able to obferve, is very different 
in common from thofe of the quadruped. In the quadruped the 
teeth are formed in the jaw, almott l'urrounded by the alveoli, 
or fockets, and rife in the jaw as they increafe in length ; the 
covering of the alveoli being abforbed, the alveoli afterwards 
rife with the teeth, covering the whole fang ; but in this tribe 
the teeth appear to form in the gum, upon the edge of the jaw, 
and they either link in the jaw as they lengthen, or the alveoli 
rife to inclofe them : this laft is moft probable, fince the depth 
of the jaw is alfo increafed, fo that the teeth appear to link 
deeper and deeper in the jaw. This formation is readily dis- 
covered in jaws not full grown ; for the teeth increafe in num- 
ber as the jaw lengthens, as in other animals. The pofterior 
part of the jaw becoming longer, the number of teeth in that 
part increafes, the fockets becoming fhallower and fhallower, 
and at latt being only a flight depreffion. 
It would appear, that they do not fhed their teeth, nor have 
they new ones formed fimilar to the old, as is the cafe with 
moft other quadrupeds, and alfo with the Alligator. I have never 
been able to deteCl young teeth under the roots of the old 
ones ; and indeed the fituation in which they are firft formed 
Vol. LXXVII. L 1 1 makes 
