68 



ANIMAL BIOLOGY 



50, A). On the sides of the shaft are the two flat surfaces 

 which make up the vane. This vane is composed of slender 

 parts called harhs that may be easily separated from each 



other, or when sep- 

 arated may be read- 

 ily united, because 

 of little hooks (Fig. 

 50, B). This the 

 bird does when it 

 smooths or "preens" 

 its feathers. 



52. Legs. — On 

 comparing the arm of 

 man with the wing of 

 a bird we found that 

 they were similar in 

 structure, and the 

 same is likewise true 

 of the leg and foot. 

 While the thigh of a 

 bird is much shorter 

 proportionately than 

 is that of man (Fig. 

 51), both have but a 

 single bone. Below 

 the knee of the. bird 

 is the shank or "drum- 

 stick" which consists 

 of a long bone ex- 

 tending to the ankle, 

 and beside it is a 

 slender bone attached only at the upper end. This region in the 

 leg of man is likewise composed of a relatively thick shin bone, on 

 the outer side of which is a thin bone extending down to the ankle. 



Fig. 51. — A, skeleton of leg of an ostrich; B, 

 ;j skeleton of leg of a man. (E. R. Sanborn.) 



