TREE HORNBILLS AND GROUND HORNBILLS 



like that of a hare or an antelope, and air spaces traverse 

 the body throughout. The bodies of all birds are 

 aerated by expansions of the lung ; but the hornbills 

 are particularly so, and the absence of fat conduces to 

 this spareness of appearance. Their flight appears 

 heavy in spite of this, and they make a great deal of 

 noise, especially at getting off, which has been compared 

 by Dr. Russell Wallace to the puffing of a steam 

 engine. It is not all hornbills that lead an arboreal 

 life. In Africa are at least two different species of 

 ground hornbills, which are rightly placed in a distinct 

 genus and termed Bucorax and Bucorvus. Their beak 

 is not quite so huge as in the more exaggerated form in 

 which it is found in Buceros and its allied tree dwellers. 

 But it is still of respectable dimensions. Bucorvus 

 sidles and prances with some stateliness, and, instead 

 of living upon fruits, catches reptiles. It is not unraven- 

 like in aspect, and is distinctly intelligent, to judge 

 from the numerous specimens which have been on view 

 at the Zoo in late years. The gait of this bird has pro- 

 duced some alteration in the structure of the foot. It 

 is still of the pattern of its tree- frequenting relatives ; 

 but the inner toe of the three forwardly- directed ones 

 has a much more massive formation than that of 

 Buceros, and is of greater length. It is noteworthy that 

 the same effect has been produced here as in man com- 

 pared with the arboreal apes. Our great toe is the 

 strongest of the toes, and bears most of the weight of 

 the foot. So in the Bucorvus it is the physiological 

 equivalent of the great toe 'which .is correspondingly 

 increased, for the real big toe is turned back. Now in 

 ungulate animals which are also digitigrade, pressure 

 upon the foot is associated with the disappearance of 

 the outer toes and the predominance of the middle toe 

 or toes. It is in some of its breeding habits that the 

 hornbill is so remarkable and different from other birds. 



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