34 R. W. SHUFELDT, 
produced backwards as a sharp spine. This is also a feature of 
the fourth cervical vertebra,in which, too, both the haemal 
and neural spines begin to be reduced, the former entirely disappearing- 
until the thirteenth cervical is arrived at, when it reappears 
as a thin, median apophysis of some size. 
Dendrocygna, in common with so many other Anatinae, has 
the centra of the fourth to the seventh cervicals conspicuously flat. 
and broad, and to a greater or less degree, this is to be observed 
in all Anseres. It is a very striking feature of the cervical 
vertebrae in Polysticta stelleri, where, in the the case of the seventh, 
eighth, and ninth cervicals, the centra below are concaved, and 
nearly as broad as long. Hypapophyses gradually appear, however, 
for the formation of carotid canals, at the extreme anterior border- 
of the centrum of each vertebra, being most complete in the twelfth 
cervical. After that, a blade-like process supplants it, which in 
turn becomes smaller on the 13th to the 15th inclusive, and tri- 
cornuate on the 16th cervical. 
In this skeleton of Dendrocygna autumnalis (454), I find a pair 
of free ribs on the 15th cervical, which are short and without epi- 
pleural processes. There is another pair articulating with the 16th 
cervical which are much longer and have the epipleurals. This 
is not the rule; for the 15th cervical in these Tree-Ducks is usually 
without them, the fused and outstanding pleurapophyses, forming the 
lateral vertebral canals, occupying their place. Long since, I have 
shown in some of my publications on the osteology of birds that, 
even in the same species, there is no hard and fast rule with respect 
to either cervical or pelvie ribs in that Class of the Vertebrata, 
and here is another instance of it (see Table above). 
The dorsal vertebrae in Dendrocygna are locked together 
in articulation with great closeness. Above, the broad, neural 
spines are practically in continuous contact by their anterior and 
posterior margins, giving the appearance of one continuous neural 
crest. Extensive ossification also takes place in the tendons of the 
muscles of the back, and these, together with the highly developed. 
metapophyses, tend still more toward the rigidity of this division. 
of the spinal column in these ducks. 
On either side, near the middle of the centrum of any one of 
these much laterally compressed dorsal vertebrae, we observe a 
pneumatic foramen in some specimens (453) that may be very small, 
or altogether absent in other skeletons, either on one side, or both. 
