72 Br. Harwood on the Structure and 



feet are observed to be furnished with still broader membranes, 

 which in many South Sea species are even extended beyond the 

 ends of the claws, whereby the extent of surface is greatly in- 

 creased ; but in all, aided by the powerful muscles of the spine, 

 these feet act with immense force on the surrounding fluid, and 

 produce an extremely rapid progression. From such external 

 characters, a beautiful connexion is at once observed be- 

 tween the seal and those aquatic animals which surround it, 

 its feet, for example, being intermediate in their structure 

 between the simply webbed ones of the otter and beaver, and the 

 flattened fin-like ones of the manati, the whales, and other ce- 

 tacious mammalia which are more exclusively adapted to a 

 watery element. But in the skeleton of the seal, these gradations 

 and adaptations are still more apparent : though composed of the 

 usual number of bones, the length and flexibility of its neck is 

 of the highest importance in its economy ; for, by the slightest 

 inclination of the head, at the end of this long lever, in any 

 direction, while diving, its centre of gravity becomes instantly 

 changed at its will ; and thus are its submarine chases, even 

 after the swift salmon, rendered so marvellously successful, 

 that its only mode of escape consists in darting into the shal- 

 lows. In the general form of the skeleton, seals bear no very 

 distant relation to the weasels, the chest having an unusual 

 extent of motion, by the free articulation of its vertebrae, and, 

 as in those animals, the liver and lungs are each divided into 

 several distinct lobes, that they may glide smoothly over each 

 other, and not oppose the great curvature to which their bodies 

 are liable. On the same principle, their ribs are placed farther 

 asunder than in most others ; while the lumbar regions and pel- 

 vis, as in all diving animals, are long and narrow, for the attach- 

 ment of powerful muscles. We now see that the limbs, 

 although so curiously shortened for aquatic operations, possess 

 the same number and arrangement of bones as those of animals 

 whose actions are terrestrial, subject, however, to interesting 

 modifications ; for instance, in the fore-feet, the thumb or inner 

 toe is the strongest, and the outer the weakest; but in the 

 hinder feet, to increase the force and extent of membranous 

 surface opposed to the water, the two outer toes are far the 

 longest and strongest. 



