Strudlure and Oeconomy of Whales. 387 
are external, the other internal. The direction of the fibres 
of the external layers is the fame as in the tail, forming a ftratum 
about one-third of an inch thick ; but varying, in this refpedt, 
as the tail is thicker or thinner. The middle layer is com- 
pofed entirely of tendinous fibres, paffing diredtly acrofs, be- 
tween the two external ones above delcribed, their length be- 
ing in proportion to thethicknefs of the tail ; aftrudture which 
gives amazing flrength to this part. 
The lubftance of the tail is fo firm and compact, that the 
vefifels retain their dilated hate, even when cut acrofs ; and 
this feftion confifts of a large veflel furrounded by as many 
fmall ones as can come in contact with its external furface ; 
which of thefe are arteries, and which veins, 1 do not know. 
The fins are merely covered with a ftrong condenfed adipofe 
membrane. 
Of the Fat . 
The fat of this order of animals, except the fpermaceti, is 
what we generally term oil. It does not coagulate in our 
atmofphere, and is probably the moll; fluid of animal fats; but 
the fat of every different order of animals has not a peculiar 
degree of folidity, fome having it in the fame ffate, as the Horfe 
and Bird. What I believe approaches neareft to fpermaceti, 
is the fat of ruminating animals, called tallow. 
The fat is differently lituated in different orders of animals ; 
probably for particular purpofes, at leaf! in fome we can affign a 
final intention. In the animals, which are the fubjedl of the pre- 
fent Paper, it is found principally on the outfide of the mufcles, 
immediately under the fkin, and is in confiderable quantity. 
It is rarely to be met with in the interftices of the mufcles, or in 
any of the cavities, fuch as the abdomen or about the heart. 
In 
