1888.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. '229 



end seems to be attached pretty much in the same way to the side of 

 the tibial shaft. This latter articulation occurs at a point about the 

 unction of middle and lower thirds of the shaft of the larger leg bone. 



fe^aseste 



Fig. 13. Sternum of Somateria dresseri ; pectoral aspect. (Specimen 16989, Smithsonian collection.) 



By the author. Life size. 



With the exception of its proximal fourth, the tar&o-metatarsus is con- 

 siderably compressed from side to side, much in the same way as we 

 find it in the Urinatorulce. and to the same 

 end. 



In order to show that this is simply an- 

 other example in the skeleton of this Mer- 

 ganser of a physiological adaptation of 

 structure to meet a certain requirement 

 demanded on the part of its habits, I have, 

 in Figs. 9 to 12, contrasted this bone, in 

 two views, with the same bone taken from 

 a specimen of the American Eider Duck, 

 a bird far less noted as an habitual diver. 

 It will be seen at a glance that fundament- 

 ally these two bones are essentially upon 

 the same plan of structure, or, in other 

 words, both are of an anserine type. The 

 hypotarsusof this bone in Mergm consists 

 of four vertical ridges— an inner large and longest one and three others 



Fig. 14. Th&furcula of Somateria dres- 

 seri : life size. (Specimen 16989, Smith- 

 sonian collection.) By the author. 



