OSTEOLOGY OF BIRDS 



271 



which the common form of domestic ducks have been derived. But 

 such a circumstance, it seems to me, is of little or no avail in a 

 treatise devoted to a general description of the osteology of the 

 wild species; or as many of them as I have at this writing. More- 

 over, I have already shown in my earlier contribution, that Spatula 

 is quite closely allied to the teals, and these latter are not included 

 in the same genus with the Mallard, the genus Anas. 



With these prefatory remarks then, I will now proceed to demon- 

 strate the skeletal characters of the Anatinae, using Spatula 

 c 1 y ]) e a t a for the purpose, and by means of my additional ma- 

 terial, make pari passu, such comparisons as appear necessary to 

 .-how probable affinities, and meet the ends of taxonomy. 



Spatula clypeata 



Compared with that of other American Anatinae 



Osteologically. and doubtless in its general structure also, Spatula 

 closely resembles the true teals. In addition to its larger size, the 

 principal character in its skeleton that differs with the correspond- 

 ing structure as seen among these birds is the enormous develop- 

 ment of its mandibles. 



In the dried skull of Spatula the premaxilla is an elegant, sym- 

 metrically formed, yet delicate scroll of bone, and, so far as I am 

 aware, unequaled by any similar structure among vertebrates. At 

 the middle part of the anterior arc there occurs a thickening, which 

 in life supports the " nail" of the integumental sheath. 



Both this and the region on either side is, externally, quite 

 thickly studded with foramina. These are minute and pierce only 

 the outer compact layer of the bone to enter the spongy tissue 

 within. 



•The external narial apertures are placed well back, each being 

 subelliptical in outline. Comparatively speaking, these openings are 

 considerably larger in the swans and geese, while in such forms 

 as Clan gu la islandica, Netta rufina, some of the 

 eiders and others, they relatively occupy a mid site on the mandi- 

 bular side, the nasal being a broader bone. 



Spatula and the teals always have the extremity of the nasal 

 median processes of the premaxillary remain distinct to a large 

 extent in the craniofacial region throughout life. This is also well 

 shown in the Mallard, less so in some species of. Somateria, being 

 entirely absent in Netta rufina. Marila and many other 

 ducks. 



