NINTH ANNUAL REPORT. 



227 



r 



FOOT OF THE APTERYX. 



ment of the eye. It, however, 

 naturally lacks the delicate 

 adjustment of the eyes of a 

 bird such as a hawk, which 

 can become near-sighted or 

 far-sighted at will. 



As in cursorial mammals, 

 the general contour of the 

 body of these birds is adapted 

 to lessen resistance to the air. 

 Yet in the present connection 

 no stress can be laid upon this 

 character, since the ratite birds 

 are descended from true birds 

 of flight, with keeled sternums 

 and a general moulding of the 

 body even more adapted for 

 swift motion through the air. 



The enormous weight of some 

 of the ratite birds is a condition 



impossible in a flying bird. A full-grown Ostrich may weigh 

 three hundred pounds ; while twenty-five pounds for a swan and 

 thirty-two pounds for a bustard are maximum weights among 

 the volant Cariiiatae. 



Any extensive mention of the skeletal adaptations would be 

 foreign to this paper, and indeed, when we study the bony frame- 

 work of the struthious birds, we find so many characters which 

 are dinosaurian and typically reptilian, that it seems as if any 

 phylogenic comparison must be with the Sauropsida as a whole, 

 rather than with Archaeopteryx or the Cariiiatae alone. 



The most important changes in the skeleton, due to the cur- 

 sorial habits of these birds, are plainly visible on the exterior. 

 One feature is the long and flexible neck, correlated with the long 

 legs. The swan is the only carinate bird which equals the Ostrich 

 in the number of cervico-dorsal vertebrae, each having twenty- 

 five. 



The tall casque, or horny helmet, of the Cassowary. sui)portod 

 bv osseus tissue within, is a special adaptation to protect the 

 bird's head from the many hanging lianas and the undergrowth 

 which it encounters when leaping and running at full speed 

 through the dense forests of its haunts. 



The flat, camel-like resting-pad of the Ostrich reveals the char- 

 acter which has given the name of Ratite to this Subclass of birds 



