60 ODONTORNITHES. 



The Sternum. (Plates VI-VIII.) 



The sternum in Hesperomis somewhat resembles in general form the 

 corresponding bone in the genus Uria, but in other respects is more like 

 that in the Batitce. It is thin and weak, and entirely without a keel. It is 

 expanded in front, especially between the costal processes, and has two 

 deep grooves for the reception of the coracoids. These grooves are 

 placed obliquely, converging anteriorly, and are widely separated from 

 each other. The sternum has a rounded mesial projection in front, which 

 is somewhat thickened, but there is no true manubrium. 



A comparison of the keelless sternum of Hesperomis, represented in 

 Plate VIII, figure 6, with that of one of the Batitce, for example, the 

 Emeu, as shown below, will make clear the resemblance in this part of 

 the structure between these two types. 



Figure 15. — Sternum of Emeu (Dromceus Nova Hollandice, Latham) ; front view ; one-half natural size. 

 a. costal process ; 1>. surface for articulation of sternal ribs ; c. groove for left coracoid. 



The sides of the sternum in Hesperomis are concave in outline, and 

 in Hesperomis regalis, there are four articular projections on each side for 

 the attachment of sternal ribs. These processes are all on the anterior half 

 of the sternum. Behind these, the lateral margins are nearly parallel. 

 The posterior end of the sternum is quite thin, and had two shallow 

 emarginations. In Hesperomis crassipes (Plate VII), the sternum repre- 

 sented is nearly perfect, and in this species there are five articular faces on 

 each side, for the sternal ribs. The posterior margin in the same species 

 is less excavated than in Hesperomis regalis. 



