404 JWk Hunter’s Objervations on the 
Befides this mode of growth, which is common to all fuch 
fubdances, it receives additional layers on die outfide, which 
are formed upon the above-mentioned vafcular fubdance ex- 
tended along the furface of the jaw. This part alfo forms 
upon it a femi-horny fubdance between each plate, which is 
very white, rifes with the whalebone, and becomes even with 
the outer edge of the jaw, and the termination of its outer 
part forms the bead above mentioned. This intermediate fub- 
dance fills up the fpaces between the plates as high as the jaw, 
a£ts as abutments to the whalebone, or is fimilar to the 
alveolar precedes of the teeth, keeping them firm in their 
places. .(See Tab. XXIII.) 
As both the whalebone and intermediate fubdance are con- 
ffantly growing, and as we mud fuppofe a determined length 
neceflary, a regular mode of decay mud be edablidied, not 
depending entirely on chance, or the ufe it is put to. 
In its growth, three parts appear to be formed; one from 
the riling core, which is the center, a fefcond on the outfide, 
and a third being the intermediate fubdance. Thefe appear to 
have three dages of duration ; for that which forms on the 
core, I believe, makes the hair, and that on the outfide makes 
principally the plate of whalebone ; this, when got a certain 
length, breaks off, leaving the hair projecting, becoming at 
the termination very brittle ; and the third, or intermediate 
fubdance, by the time it rifes as high as the edge of the fkin 
of the jaw, decays and foftens away like the old cuticle of the 
lole of the foot when deeped in water. 
The ufe of the whalebone, I fhould believe, is principally 
for the retention of the food till fwallowed ; and do fuppofe 
the fifh they catch are fmall, when compared with the fize of 
the mouth. 
5 
The 
