Structure and 0 economy of Whales. 37 7 
and the organs of digeftion ; all which either a£t, or are a&ed 
upon, by external matter. 
This variation, from external caufes in many infhmces in- 
fluences the fhape of the whole, or particular parts, even 
giving a peculiar form to fome which belong to the fir ft order 
of actions, as the heart, which in this tribe, in the Seal, Otter, 
&c. is flattened, becaufe the cheft is flattened for the purpofe 
of fvvimming. The contents of the abdomen are not only 
adapted to the external form ; but their direction in the cavity 
is, in fome inflances, regulated by it. The anterior extremity, or 
fin, although formed of diftinft parts, in fome degree fimilar 
to the anterior extremities of fome quadrupeds, being com- 
pofed of fimilar bones placed nearly in the fame manner, yet 
are fo formed and arranged as to fit them for progreflive 
motion in the water only. 
The external form of this order of animals is fuch as 
fits them for dividing the water in progreflive motion, and 
gives them power to produce that motion in the fame manner 
as thofe flfh which move with a conflderable velocity. On 
account of their inhabiting the water, their external form is 
more uniform than in animals of the fame clafs which live 
upon land, the furface of the earth on which the progreflive 
motion of the quadruped is to be performed being various and 
irregular, while the water is always the fame. 
The form of the head or anterior part of this order of animals 
is commonly a cone, or an inclined plane, except in the Sperma- 
ceti Whale, in which it terminates in a blunt furface. This form 
of head increafes the furface of contact to the fame volume of 
water which it removes, leflens the preflure, and is better 
calculated to bear the reflftance of the water through which 
the animal is to pafs ; probably, on this account, the head 
H h h 2 is 
