Teeth of Cartilaginoys Fifer. 28y 
wanting their angles to the right, and the teeth on the right- 
fide being deftitute of. their angles to the left. | 
As it is certain, that the anterior teeth were formerly pofte- 
rior ones, and as the teeth in each .rew were all deficient in one’ 
angle, it follows, that they muft have been formed pofterior to 
the infertion..of this extraneous body. Again, if we allow 
that before the accident the animal was in poffeflion of perfe& 
teeth, it follows alfo, that they were coniumed and ee 
by imperfect ones. : 
There were fix teeth in each row, and fifty-two rows,’ 
making together about 312 teeth. Now allowing the con- 
f{umption to have been equal in all: parts of the jaws, it fol- 
lows, that the animal had already confumed 312 teeth, and 
was in pofleffion of a like number for future confumption. 
The teeth of fharks, rays, &c. may be divided into active 
and paffive. The active teeth are the anterior ones of each 
row, ftanding with their points upwards. The paflive tecth 
are the remaining ones, lying ane upon another, like the tiles 
upon a houfe (imbricated), with their points downwards.’ It 
appears from the foregoing account, that the anterior or active 
teeth had been replaced fix times; and that they might have 
been renewed fix times more, making in all twelve times. 
From which, I think, we may reafonably conclude, that this 
‘does not happen any precife number of times; but that the 
renovation is perpetual during the life of the animal. 
The longevity of fifhes is a fact pretty well eftablifhed. In 
addition to this part of natural knowledge, I have endeavoured 
to prove, that a part of the inhabitants of the great deep tre- 
tain, in the article of teeth, a perpetual juvenility, being appa- 
tently utter ftrangers to edentulous old age. 
Vou. LXXLY. P p © XPLA- 
