518 



APPENDIX. 



is never any mixture of those parts which are 

 essential to life, nor in their different modes of 

 sensation. 



The external form of this order of animals is 

 such as fits them for dividing the water in pro- 

 gressive motion, and gives them the power to pro- 

 duce that motion in the same manner as those 

 fish which move with a considerable degree of ve- 

 locity. On account of their inhabiting the water, 

 their external form is more uniform than in ani- 

 mals of the same class which live upon land ; the 

 surface of the earth, on which the progressive 

 motion of the quadruped is to be performed, 

 being various and irregular, while the water is 

 always the same. 



The form of the head or anterior part of this 

 order of animals is commonly a cone, or an in- 

 clined plane, except in the Spermaceti Whale, in 

 which it terminates in a bkmt surface. This 

 form of head increases the surface of contact to 

 the same volume of water which it removes, lessens 

 the pressure, and is better calculated to bear the 

 resistance of the water through which the animal 

 is to pass : probably on this account the head is 

 larger than in quadrupeds, having more the pro- 

 portion observed in fish, and swelling out laterally 

 at the articulation of the lower jaw: this may 

 probably be for the better catching their prey, as 

 they have no motion of the head on the body ; 

 and this distance between the articulations of the 

 jaw is somewhat similar to the Swallow, Goat- 

 sucker, Bat, &c. which may also be accounted 



