ORGANS OF LOCOMOTION. 



85 



across them, so as to sorve the purpose of a wing. In birds, 

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

 which are soldered together, and destitute of nails ; and the 

 thumb is rudimentary. 



176. The arm of the turtle (Fig. 40) is peculiar in having, 



Fig. 41. 



a 



Fig. 42. 



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 enor- 

 mous 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 ; the elbow projects backwards, and the hand 

 is excessively large and stout. 



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

 so peculiar, that it is often difficult to trace their correspond- 

 ence to all the parts found in other animals ; nevertheless, 

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

 8 



