LOCOMOTION. 225 



the bag communicates with the large air cells on 

 the back of the neck*, and therefore we may fairly 

 conclude it is intended to render the birds light and 

 buoyant for running, since they are too heavy to fly 

 without considerable difficulty. 



These birds are remarkable for the length of their 

 legs, which must be very advantageous for swiftness 

 of running ; but it would be wrong to infer as a 

 general principle that all birds with long legs are 

 swift-footed. On the contrary, the wading birds 

 (Gr allator es, ILLIGER), which have proportionably 

 much longer legs than the ostrich or the bustard, 

 are not well adapted for walking on land. Amongst 

 these the flamingo (Phcenicopterus ruber) is one 

 of the longest-legged birds, yet it is in this respect 

 far exceeded by the stilt (Himantopus melanopterus, 

 MEYER), and the legs in the latter are besides slender, 

 and even " so flexible,'' as Wilson says of the Ame- 

 rican stilt, " that they may be bent considerably 

 without danger of breaking t," as if, in accordance 

 with Pliny's name (Himantopus), they had been cut 

 out of a thong of leather J. Aldrovand mentions its 

 pace as slow and laborious ; and White of Selborne 

 says, " it must be matter of great curiosity to see it 

 move ; to observe how it can wield such a length of 

 lever with such feeble muscles as the thighs seem 

 to be furnished with. At best one should expect it to 

 be but a bad walker : but what adds to the wonder 

 is, that it has no back toe. Now without that steady 

 prop to support its steps, it must be liable in specu- 

 lation to perpetual vacillations, and seldom able to 

 preserve the true centre of gravity ." The truth 

 is that the legs are not formed for walking, but for 

 wading ; and we have the testimony of Wilson that 



* Comp. Anat. i. 278. f Amer. Ornith. vii. 55. 



J Oppian, de Aucup. ii. Letter 91. 



z 



