392 A HISTORY OF BIRDS 



{Phcsthon), are indicative of a primitive condition, where these 

 meet in front of the acetabulum of a speciaHsed or adaptive 

 condition. In support of this view it may be mentioned that, 

 while in many of the Fruit-pigeons, for example, which walk 

 but little, the innominate bones are widely separate one from 

 another, in the great Goiira Dodo and Solitaire these bones 

 meet one another in front. 



Certain extraordinary features in the pelvis of the Rhea 

 may find brief mention in these pages, if only that they may 

 excite further study. Briefly, then, the post-acetabular ilia have 

 approached one another so closely that they have brought about 

 the atrophy of so much of the vertebral column as is embraced 

 between them, all that remains of this being represented by 

 mere vestiges of vertebrae. The free caudals are fairly well de- 

 veloped. Since in some specimens more or fewer of the vesti- 

 gial caudals have disappeared, we have the unique condition 

 of a discontinuous vertebral column ! Further, in the pelvis of 

 Rhea alone do we find the ischia meeting one another in the 

 middle line throughout their whole length, forming a chamber 

 enclosing the kidneys ! 



The effect of a cursorial habit on the legs has been chiefly to 

 reduce the toes, first in length, then in number. 



The leg of the Ostrich {Siruthio) affords the most striking 

 instance of this numerical reduction. As is well known, only the 

 middle and outer toes now remain. Of these the middle is by 

 far the largest ; the outer indeed shows unmistakable signs of 

 still further reduction, inasmuch as the claw has disappeared. 

 This limb is a striking parallel to that of the horse's. But it 

 differs in this respect, that whereas in the horse the weight of 

 the body is borne on the terminal phalanx, in the bird all the 

 phalanges are applied to the ground. The Bustards are ex- 

 tremely short-toed birds and have only three toes. 



As with the pelvis, there are some curiously contradictory 

 facts to be explained. Thus, how is it that the JVIoas have 

 retained the hallux while all the other Struthious birds save 

 Apteryx have lost it ? The wings in the Moas from disuse have 

 absolutely disappeared, yet the equally useless hind toe sur- 

 vived ! 



Though the majority of living birds spend a considerable 

 portion of their lives amid trees or scrub, adaptations to a 



