500 ADAPTATION OP EXTREMITIES FOR SWIMMING. 



the spreading-out of the fingers, and their union by means of a 

 fold of skin which is stretched over them ; as the web of a 

 swimming Bird is stretched over its toes, so as to make an 

 oar or paddle of sufficiently wide surface. This is the ease, 

 for example, in the Ornithorhyncus of Australia, and in the 

 Otter of our own country. When the members are intended 



Fig. 240. SKELETON OF SEAL. 



vc, cervical vertebrae, vd, dorsal vertebrae; vl, lumbar vertebrae; vs, sacral vertebras; 

 vq, caudal vertebrae ; b, pelvis ; s, sternum; h, humerus; r, radius ; ca, carpus ; 

 me, metacarpus ; ph, phalanges ; o, scapula ; c, ribs ; /, femur ; r, patella ; t , tibia ; 

 ta, tarsus ; mt, metatarsus ; ph, phalanges. 



exclusively for swimming, however, they undergo more con- 

 siderable modifications in structure. The parts corresponding 

 with the arm and fore-arm are very short, and the movements 

 of the hand are thus limited, but they can be accomplished 

 with all the more force. But the bones of the hand are large 

 and spread asunder, and are enclosed in a firm integument 

 which may even cover their extremities. Sometimes the 

 number and arrangement of these bones are precisely the 

 same as in the hand of Man ; this we see in the Seal (fig. 240), 

 where their extremities are furnished with separate claws that 

 project beyond the integument. Sometimes the number of 

 phalanges in the fingers is considerably increased, as in the 

 Whale ; and in other instances, the fingers are replaced by a 

 multitude of small rods of bone, enclosed within a continuous 

 skin, such as we see in the fins of Fishes (fig. 243). 



665. In the Seal, which does not depart widely in its 

 general construction from land quadrupeds, the hind feet are 

 formed upon the same plan as the fore ; but they are carried 



