OSTEOLOGY OF BIRDS 



297 



lateral xiphoid processes broader than is usually the case among 

 the river ducks, while the " notches " are smaller and nearly closed 

 in posteriorly. They have the same elliptical outline, however, and 

 the three xiphoid prolongations are about of an equal length, and 

 the keel reaches nearly to the end of the sternal body, behind. 



Among the eiders of the genus Somateria it becomes very broad 

 and in Somateria d r e s s e r i is likewise short [sec fig. 27] . 

 It is here, as in most, if not all, ducks, completely nonpneumatic, 

 with seven facets on each border for the costal ribs. All three of the 

 xiphoid prolongations are also broad, and in S . m o 1 1 i s s i m a 

 and S . v. nigra the lateral ones extend somewhat beyond the 

 middle one behind, and have their free ends slightly expanded. A 

 manubrium is but very feebly developed, and the carina extends 

 nearly the entire length of the sternal body. The summit of either 

 costal process curls gently outward, and in S . v . nigra the 

 coracoidal groove is continuous, being of quite uniform depth and 

 hight. 



Oidemia perspicillata has a sternum of a pattern re- 

 sembling the eiders in all essential particulars, but this does not 

 hold quite true for a much larger bird of the same genus, or the 

 White-winged scoter (O. deglandi), it being a duck with 

 a very broad sternum, especially behind, where the lateral xiphoid 

 processes are narrow, flaring somewhat outward, and have bluntly 

 pointed free ends. The " notches " are well opened behind, but 

 otherwise present nothing peculiar, being like the eiders. 



The carina in the scoters passes nearly the entire length of the 

 body of the bone, and its angle in front is but moderately acute, and 

 so not very projecting. Oidemia americana has a sternum 

 very like this but is smaller, belonging as it does, to a smaller 

 species. 



MODIFICATIONS OF THE LARYNX AND TRACHEA AMONG 



THE DUCKS 



Not a little has been contributed to this interesting subject by 

 Eyton, by Yarrell, by Garrod, and by others. A number of these 

 contributions are illustrated by excellent figures showing the ex- 

 traordinary variations of the lower larynx and trachea among the 

 Anseres. Macgillivray and Forbes both left some excellent work 

 in this direction. Owen figured the lower larynx of both M e r - 

 gus serrator and Mergus merganser, and re- 



