OSTEOLOGY OF BIRDS 



on either side, from the lip of the bone that overarches the outer 

 end of the coracoidal groove, to pass along the inner side of the 

 vacuities behind, where they become very faintly marked. 



A transverse straight line limits the xiphoidal extremity, and in- 

 grafted upon this in its middle we find a distinct convex prolonga- 

 tion of no great size, its base being rather less than one third of 

 the border upon which it occurs. 



Just over this latter, in the apertures of the posteroexternal angles 

 of the bones, we find on either side a large, oval fenestra. 



A sternum of this shape, differing as it does in this particular 

 from the notched style of the bone among most of the geese and 

 ducks (for it is the same as we find it in Clangula), forms an 

 exception to the character laid down by Huxley for his Cheno- 



' Fig. 4 Sternum of M erg us serrator; right lateral view, natural size. Drawn, 

 by the author from specimen no. 16626, United States National Museum Collection 

 (Compare with figure 3; same skeleton) 



morphae, which includes the subfamily to which Mergus belongs 

 [fig- 3l- 



The extensive coracoidal beds of the anterior border are sepa- 

 rated by a pit in the median line, and not a vestige of such a thing 

 as the manubrium is to be seen. 



From the pit just mentioned to the far projecting carinal angle 

 a straight osseous welt is raised, above which the anterior margin 

 is convex and sharp. 



The keel itself is low and extends clear back to the hinder margin 

 of the bone proper; its inferior border is thickened and gently con- 

 vex throughout its extent. 



A very good example of the appearance of the sternum among 

 the ducks is seen in thai of the American eider (S. dresseri). 

 In this form the profoundly two-notched hinder portion is well 

 shown, and here, too, we observe that the anterior part of the keel 



