ORGANS OF LOCOMOTION. 



85 



across them, so as to serve 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. 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 forwa~ds; 

 the fingers are long, and widely separated. In the Sloth, 

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

 elongated, and at the same time very slender ; the hand is 

 likewise very long, and the fingers are terminated by enoi- 

 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. <^/ r 



177. In fishes, the form and arrangement of Hke bonos 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 



