96 INTRODUCTION. 



fourth of four phalanges : but these may, perhaps, vary ; for Cuvier assigns 

 nine to the second, and five to the third finger. In one species of Dol- 

 phin the second finger has been found to consist of eleven, and the third 

 of eight phalanges ; the thumb (or its analogue) of three, and each of the 

 two other fingers of two. 



The structure of the flat paddle of the Cetacea will bring to mind 



the similar organs possessed by those strange extinct reptiles, the Plesi- 



IQI 102 osaurus and the Ichthyosaurus 



(figs. 101, 102), whose fossil 

 relics, discovered in the lias 

 deposit, excite our admiration 

 and astonishment, and throw us 

 back upon a distant epoch, 

 when the land and the waters 



Paddle of the Plesiosaurus. Paddle of the Ichthyosaurus. teemed With raCCS which haVC 



long disappeared from the face of the globe. 



In their organization for an aquatic mode of life, the Seal tribe approach 

 the Cetacea. They possess, however, a posterior, as well as an anterior 

 pair of limbs ; and, though the absence of clavicles limits the freedom of 

 the short humerus, they can crawl along the shore, or scramble up the 

 ledges of rocks, or icebergs. 



103 -x?53f\ The illustration (fig. 103) represents 



the osseous structure of the paddle, or 

 flipper, of the Seal. The carpal por- 

 tion, d, is broad, but so compressed as to 

 occupy but a trifling space between the 

 bones of the fore-arm, 6 and c, and those of 

 the metacarpus, e. The metacarpal bones, 

 e, five in number, are large, and decrease 

 gradually from the first to the last. Of the fingers, /, the first (the ana- 

 logue of the thumb) exceeds the rest in length : it consists, however, of 

 only two phalanges ; the other fingers, which decrease gradually in length, 

 are composed of three. 



The paws of these animals, though expressly made for swimming, are 

 not, it is evident, so truly paddle-like as those of the Whale or Porpoise : 

 the anterior pair are plainlv divided into strong toes, armed with nails, 

 and webbed : the posterior limbs are feeble ; but the toes are still distin- 

 guishable, and serve as supports to a large extent of web, constituting an 

 apparatus admirably adapted for propelling the animal through the 

 water, and calling to mind the feet of the Diver (Colymbus), or Great 

 Auk (Alca impennis), both as to appearance and position. 



This rapid survey of the hand of Man, and its analogue in the lower 

 Mammalia, leads, next, to a consideration of the inferior extremities. 



