AQUATIC MAMMALS 



ming organ (feet and tail) would present the requisite lunate form 

 the feet would have to be held back to back, instead of palm to palm, 

 and this is either impossible or would at least require changes in posture 

 which would be conspicuous externally. Of course there may be some 

 idiosyncrasy about the swimming of this animal for which a non-lunate 

 propulsive organ, and one with a longer upper than lower border would 

 be advantageous; and this must be entertained as a possibility, but it 

 is hardly likely. 



If the above arguments be correct, it seems that the only way left for 

 the sea otter to swim efficiently with its existing equipment is to place 



Figure 47. Lateral view of the left hind limb musculature of the insectivore 

 otter Potomogale, redrawn from Dobson. 



the feet horizontally to the rear, one upon either side of the tail, sole 

 up, and oscillate them in the vertical plane on the same principle that 

 the whale uses its flukes. It is true that no other mammal is known 

 ever to have employed this method of swimming and accordingly there 

 are doubtless those who will claim that it is illogical, but on the con- 

 trary it appears to be a more logical method of swimming than that 

 now employed by the seal. The external details of the sea otter support 

 this presumption. The long fifth toes would form the outer borders 

 of the swimming organ, as they should, and the tail, of almost if not 

 quite precisely the length of the extended feet, would comprise a 

 strengthening, central element. The whole would accordingly present 



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