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TEXT-BOOK OF ZOOLOGY 



perform long journeys, often through the most barren deserts, in order 

 to tind a more hospitable region. Accordingly, the ostrich must be 

 capable of easy and rapid progress. 



2. Of ftif/ht, the mode of motion of birds par excellence, the ostrich 

 is, however, incapable, for — 



(a) The great weight of the body alone (up to nearly 170 pounds) 

 would render flight extremely difficult ; whilst 



(b) The weakness of the wings and the absence of flight-feathers as 

 well as of steering-feathers, or rectrices, renders flight impossible ; for the 

 large feathers of the wings and tail have soft, flexible shafts, whilst the 

 barbs, having no hooks, are wholly disconnected, and instead of forming a 

 continuous surface (seep. 148), give the vane a frayed appearance (plume). 

 In the male these feathers are of a dazzling white colour, the body 



being covered with 

 feathers of similar 

 form, but of a deep 

 black. The plu- 

 mage of the female 

 is a brownish-grey, 

 the plumes of the 

 wing and tail being 

 dingy white. 



(c) In corre- 

 spondence with the 

 incapacity for 

 flight, we find that 

 the bones consti- 

 tuting the shoulder- 

 girdle (see p. 141) 

 are in part rudi- 

 mentary, the sternum is small and weak and without keel, and the pectoral 

 muscles which actuate the wings are feebly developed. 



3. The incapacity for flight, however, is counterbalanced by enormous 

 running powers, the ostrich being able to outstrip the fastest racehorse. 



(a) The legs are very tall (tarso-metatarsus long; the paces from 

 7 to 10 feet in length). They are naked, with the exception of a few 

 bristles at the lower portion of the thigh. A covering of feathers would 

 impede the bird in running. (Compare breeds of fowls with feathered 

 legs, so-called " stockinged " birds.) The thighs are extremely muscular 

 (cursorial legs). 



(b) The legs, moreover, arc articulated at the middle portion of the 

 trunk, so that the latter acquires a horizontal position, the bird being 





Afiucan Osthicii. 

 (The bird in the foreground about one-fiftieth natural size.) 



