“Tree-Ducks” of the genus Dendrocygna. 43 
fossa is not present in Olor, while in Dendrocygna none of the fore- 
going characters are present, the coracoid in that locality being 
either flat, or very slightly raised, with thin, lower border, and non- 
pneumatic. It is flat in Aix sponsa, or, as in Aöx galericulata, a pit 
may be present in that locality. Cereopsis in this regard agrees 
with other Anserinae. It is slightly raised in Ohenonetta jubata; 
but the coracoid in that species is non-pneumatie as in all ducks 
which I have examined.') 
At the distal end of the coracoid in Dendrocygna there are 
two facets for articulation with the sternal groove, on the 
anterior border of the sternum. When thus naturally articulated, 
on either side, the long axis of the coracoid is about in the same 
plane with the surface of the body of the sternum of the same side; 
and were the imaginary lines, representing the long axes of both 
coracoids, produced, — the bones being normally articulated, — they 
would intersect at a short distance posterior to the anterior border 
of the sternum, and somewhat above the dorsal surface of the 
sternal body. 
At the expanded sternal extremity of a coracoid of Dendrocygna 
we note a short, antero-posteriorly concaved facet at its anterior 
mesial angle. This is intended for articulation with a similar facet 
on the lower lip of the coracoidal groove of the sternum. There is 
also an elongated concave facet on the posterior aspect of the 
expanded lower end of the coracoid, bounded by the border below, 
that runs to the outer angle, with an average width of a few milli- 
meters. This is likewise intended for articulation with the sternum 
at the upper lip of its coracoidal groove of the same side. Now 
this posterior coracoidal facet in Dendrocygna in divided into 
two by a faint line running parallel to the inferior, free border of 
the bone. The lower portion of the divided facet is carried out to 
I!) In the left coracoid of a skeleton of Branta canadensis (Coll. U. 
S. Nation. Mus., No. 17980) the ligament, passing from the precoracoid 
process of the left coracoid to the sternum — the sterno-coracoidal 
ligament — has become ossified for the distance of a centimeter at 
its coracoidal end, the ossification forming a sharp, spine-like process, 
thoroughly coossified with the bone and directed downwards. A similar 
ossification took place, with respect to the ligament of the opposite side, 
on the right coracoid, but the spine is broken off. The disposition for 
this ligament to ossify in very old individuals is evident in other skeletons 
at hand, as in the case of Üereopsis. 
