144 MARINE SAURIANS. 



animal, moving rapidly through the sea, and breathing air, 

 must have required great modification of the fore-leg and 

 foot of the Lizard, to fit it for such cetaceous habits. The 

 extremities were to be converted into fins instead of feet, 

 and as such we shall find them to combine even a still 

 greater union of elasticity with strength, than is presented 

 by the fin or paddle of the Whale. Plate 12, Fig. 1, shows 

 the short and strong bones of the arm (e,) and those of the 

 fore-arm (f, g ;) and beyond these the series of polygonal 

 bones that made up the phalanges of the fingers. These 

 polygonal bones vary in number in different species, in some 

 exceeding one hundred ; they differ also in form from the 

 phalanges both of Lizards and Whales ; and derive, from 

 their increase of number, and change of dimensions, an 

 increase of elasticity and power. The arm and hand thus 

 converted into an elastic oar or paddle, when covered with 

 skin, must have much resembled externally the undivided 

 paddle of a Porpoise or Whale. The position also of the 

 paddles on the anterior part of the body was nearly the 

 same; to these were superadded posterior extremities, or 

 hind fins, which are wanting in the cetacea, and which 

 possibly make compensation for the absence of their flat 

 horizontal tail : these hind paddles in the Ichthyosaurus are 

 nearly by one half smaller than the anterior paddles.* 



Mr. Conybeare remarks, with his usual acumen, that 

 " the reasons of this variation from the proportions of the 

 posterior extremities of quadrupeds in general, are the same 

 which lead to a similar diminution of the analogous parts in 

 Seals, and their total disappearance in the cetacea, namely, 

 the necessity of placing the centre of the organs of motion, 

 when acting laterally, before the centre of gravity. For the 

 same reason, the wings of birds are placed in the fore part 

 of their body, and the centre of the moving forces given to 



* In the Ornithorhynchus, also, the membraneous expansion, or tteb of 

 the hind feet, is very much less than that on the fore-foot. 



