OSTEOLOGY OF BIRDS 



293 



In Spatula it possesses quite a prominent, peglike manubrium, 

 and its sharp, anterior carinal border slopes to the front, forming 

 an acute angle with the convex and ribbed inferior margin of the 

 keel at their point of intersection. 



This keel extends the entire length of the sternal body, and is 

 withal rather a deep one. The usual swell that fortifies it in front 

 is uncommonly broad. Above the manubrium, in front, the cora- 

 coidal grooves unite in the median line, and the common bed thus 

 formed is carried out laterally, on either side, to a point opposite 

 the middle of the base of the costal process. These latter projec- 

 tions are rather lofty and prominent, each being of a broad, quadri- 

 lateral outline. 



Either costal border occupies less than half of the lateral margin, 

 the remainder being somewhat curved and cultrate. 



Fig. 24 Left lateral aspect of the sternum of Spatula clypeata. Natural size 



Regarding this bone from a pectoral aspect, we notice that the 

 form of the sternal body is oblong, with a slight outcurving of 

 the lateral xiphoid processes behind. These latter form the 

 external boundaries to the large subelliptical vacuities, one on either 

 side of the hinder extremity of the bone ; but they fail to convert 

 these apertures into true fenestrae, from the fact that their inturned 

 tips never reach the external angles of the mid xiphoid prolonga- 

 tion [see fig. 25]. This latter projection always has its posterior 

 margin fortified by a raised and thickened edge, which is con- 

 tinuous with the rib of the inferior carinal border. 



The principal muscular line seen upon either side of this wall 

 of the sternum extends directly from the middle point of that lip 

 of bone which underlaps the outer end of the coracoidal groove, 

 to follow the inner edge of the xiphoidal notch to the apex of the 

 posteroexternal angle of the mid projection, traveling the entire 

 length of the sternum, of course, to do so. 



