CHAPTER IY. 



THE SHOULDER GIRDLE AND RIBS OF HESPERORXIS. 

 (Plates VI-IX and XX.) 



The scapular arch of Hesperomis presents several very interesting 

 features, and shows a wide divergence from the normal type in existing 

 acmatic birds. Viewed as a whole, it has but little functional importance, 

 and indicates a degradation of structure before unknown in this group 

 of birds. It throws much light, however, on the past and present forms of 

 flightless birds, both the denizens of land and of water. Its contrast with 

 the powerful pelvic arch is especially noteworthy. 



In its more important characters, the shoulder girdle of this genus 

 shows an approach to that of the Ratitce, or birds allied to the Ostrich. 

 Some of these characters hint at reptilian affinities, while others are merely 

 adaptive, and connected directly with the lack of wings. The most marked 

 points of resemblance to Struthious birds, in this part of the skeleton, are 

 the following: 



1. The sternum is devoid of a keel. 



2. The long axes of the adjacent parts of the scapula and coracoid 

 are parallel, or identical. 



These two most striking features are especially characteristic of the 

 Ratitce, according to Huxley, in the memoir already cited. 1 



'Proceedings Zoological Society, 1867, p. 418. 



