Teeth of Cartirginous Fifoes. 279 
OF THE TEETH OF CARTILAGINOUS FISHES. 
When Sreno examined the teeth of the fhark, he was fur- 
prifed to find a great number of them placed on the infide of 
each jaw, lying clofe to the bone, and many of them buried 
in a loofe fpongy flefh; conciuding that thefe internal teeth 
could be of little or no ufe to the animal. Mr. Herissanr * 
afterwards fhewed the ufe of thefe internal or pofterior teeth, 
by proving, that as the anterior teeth of each row are broken 
off, drop out, or wear away, the pofterior ones come forward 
to fupply their places +. 
But though it be certain that the anterior teeth, when loft, 
‘are replaced by the pofterior ones, neither of the above natura- 
lifts, or any other that I know of, have attempted to afcertain 
how often this circumf{tance happens. Whether the renova~ 
tion be perpetual during life ; or whether that operation be fuf- 
pended after a limited number of teeth have been fupplied. 
From a fingular circumftance, which 1 met with fome 
time ago, I am inclined to think the former is the fact; or, 
that in cartilaginous fifhes, fuch as fharks, rays, &c. there is 
a perpetual renovation ‘of the teeth. 
Being engaged in diffedting the jaws of a very- large fark I 
was furprifed to find a portion of that fharp, bearded /bone 
found in'the tail of the fire-flaire, or fting-ray {, driven quite 
- * Bowaxe Dittionaire d’Hittoire Naturelle, ‘article Requien, 
'{ Itumay-not ‘be improper on this oe¢afion to point out a miftake whiclnfome 
@aturalifts have*fallen into, in-allowing a et of mufcles for raifing the numerous 
teeth. placed. in the,jaws.of fharks. 1 have frequently diffected the jaws of thofe 
animals, and am certain no fuch muicles exift, nor are they indeed at all neceflary. 
f Raia Paftinaca Linn x1. “The French naturalifts, on account e the bone 
Gn'the tail, “CAN tis Ath Radic’ bajonnette ' 
“through 
