1888.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 223 



Of the shoulder girdle (Fig. 5). — Most Ducks, and I believe all the 

 Mergansers, have a non-pneumatic pectoral arch. It is the case in our 

 present subject, and in a number of the former at my hand. 



The furcula typifies the broad U arch in 

 Mergus, where the curve is continuous and 

 unchecked by the presence of a hypoclei- 

 dium. 



The bone is, as a whole, slightly curved 

 backward, so each limb presents a convex- 

 ity to the front; these become broader and 

 laterally compressed as we pass in the direc- 

 tion of their free extremities. 



Either head very gradually tapers off to a 

 point, and these produced ends ride over the 

 scapuhe when the arch is articulated. 



Projecting from their upper borders we 

 find a single distinct, and vertical process of 

 bone that is quite characteristic. In the 

 Eider tbis is in cartilage, but otherwise the 

 fourchette is formed in this Duck very much 

 the same as in the Merganser. (Fig. 14.) 



In a coracoid we find the summit of the 

 bone much produced above its articulation 

 with the scapula, and compressed in the 

 same plane with the shaft below it in such 

 a manner that when articulated with the 

 sternum the front of the bone is directed 

 forward and outward. 



The sternal extremity of the bone is very 

 much expanded, and it also is found in the 

 same plane with the general compression of 

 the shaft. 



Behind it is scarred by muscular lines, 

 and shows a large 1 uniform facet for the 

 groove on the sternum. 



The scapular process of. the coracoid is to 

 a great extent aborted; its superior margin 

 beiug insufficient to accommodate the entire width of the scapula. 



^Nothing of importance distinguishes the glenoid cavity, it beiug 

 formed, as in most birds, in the proportion of one-third on the part of 

 the scapula and the remainder by the bone under consideration. 



The scapula is much arched, and nearly of an equal width the entire 

 length of its blade, its apex being rounded off. We find the bone con- 

 siderably compressed in the vertical direction throughout, and the 

 length of the chord measured between its extremities less than the 

 length of the coracoid. 



Fig. 4. Sternum of Mergvs ser- 

 ralor,- right lateral view ; life size. 

 By the author, from specimen 16G26, 

 Smithsonian collection. 



