2 R. W. SHUFELDT, 
portion of the bone anteriorly. The infero-external border of the 
palatine is also sharp, terminating at the angle behind in a distinct 
process, and is, for its entire, length, concaved inwards. These 
bones have an extensive interarticulation posteriorly, and here, either 
one of them develops a delicate spur that, for a greater or less 
distance, fuses with and forms the upper, rounded margin of the 
vomer; in the skulls of adult Anseres, the fusion between the 
two is usually complete, with all sutural traces obliterated. This is 
not invariably the case, however; for in the skull of an adult Pacific 
Eider at hand, these palato-vomerine sutures can be easily made 
out though their fusion is quite complete. 
In Dendrocygna autumnalis, and doubtless in all others of the 
genus, the vomer is an elongated lamina of bone, very thin from 
side to side, and arched, so that its thickened, upper, palato-vomerine 
border is convex from end to end, — the lower, sharpened one being 
correspondingly concaved. The thickened superior margin is produced 
anteriorly as a sharp, little spine, which usually rests either upon 
the fused maxillo-palatine mass directly in front of it, or coössifies 
with the same, or, finally, may not reach that far at all, but freely 
projects into the postero-rhinal chamber. This is the rule for the 
anterior extremity of the vomer throughout the Anseres, where 
its morphology will be found to be much the same; though in some 
species interesting differences are to be observed, and these will be 
noted further on. 
Dendrocygna has the general concavity, on this nethermost aspect 
of the superior mandible, very profoundly concaved, with its sharp 
tomial margins quite parallel to each other. This is the case in 
Anas; but here the concavity is not as deep, proportionally, while 
the external margins diverge very slightly as they proceed forwards. 
In Spatula, this divergence is great, for the reason that the elegant 
scroll-like osseous superior mandible in this duck is so marvellously 
expanded at its distal extremity. 
Both in Anas and Dendrocygna there is a subelliptical foramen 
of very considerable size in the mandibular roof, it being situated 
mesially in the posterior third of the space in question. It opens 
into the rhinal chamber, opposite the external narial apertures above. 
Its extent and form varies greatly throughout the Anseres. For 
instance, in Erismatura jamaicensis, it may be nearly obliterated by 
the extension forwards of the maxillo-palatine mass and the greater 
amount of ossification of the premaxillaries (Fig. 33 Pl. 6). 
