ORGANS OF LOCOMOTION. 



61 



stretched, so as to serve the purpose of a wing. In birds, 

 the pigeon, for example, (Fig. 39), there are but two fin- 

 gers, which are consolidated and destitute of nails ; and the 

 thumb is rudimentary. 



176. The arm of the turtle (Fig. 40) is peculiar in hav- 



a 



d 



Fisr. 41. 



Fig. 42. 



ing, besides the shoulder-blade, two clavicles ; the arm-bone 

 is twisted outwards, as well as the bones of the fore-arm, so 

 that the elbow, instead of being behind, is turned forwards; 

 the fingers are long and widely separated. In the Sloth 

 (Fig. 41), the bones of the arm and fore-arm are very 

 greatly elongated, and at the same time very slender ; the 

 hand is likewise very long, and the fingers are terminated 

 by enormous non-retractile nails. The arm of the mole, 

 (Fig. 42), is still more extraordinary. The shoulder-blade, 

 which is usually a broad and flat bone, becomes very 

 narrow ; the arm-bone, on the contrary, is contracted so 

 much as to seem nearly square ; and the hand is exces- 

 sively large and stout. 



177. In fishes, the form and arrangement of the bones is 

 so peculiar that it is often difficult to trace their analogy to 

 all the parts found in other animals ; nevertheless, the 

 bones of the fore-arm are readily recognized. In the 



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