. Animal physiology. Physiology, Comparative; Physiology, Comparative. ADAPTATION OF EXTREMITIES FOR SWIMMING. 489 atmosphere, as in flight, requires a considerable expenditure of power to keep it up ; and the yielding nature of the element prevents the propelling organs from acting against a firm sur- face ; but the onward movement, in consequence of the slight resistance, is easily accomplished. 664. When the feet of a Quadruped are to serve both as walking and swimming organs, the end is accomplished by the spreading of the fingers, and their union by means of a fold of skin, which is stret
. Animal physiology. Physiology, Comparative; Physiology, Comparative. ADAPTATION OF EXTREMITIES FOR SWIMMING. 489 atmosphere, as in flight, requires a considerable expenditure of power to keep it up ; and the yielding nature of the element prevents the propelling organs from acting against a firm sur- face ; but the onward movement, in consequence of the slight resistance, is easily accomplished. 664. When the feet of a Quadruped are to serve both as walking and swimming organs, the end is accomplished by the spreading 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 case, for example, in the Ornithorhyncus of Australia (Fig. 101) ; or in the Otter of our own country. When the members are intended exclusively for swimming, however, they undergo more considerable 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 pre- cisely the same as in the hand of Man ; this we see in the Seal, 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. Fig. 226.—Seal. 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. (See Fig. 38.) In. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the origi
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