rtebra, making ten pairs of ribs; but these ten ribs do not
correspond, or arise from the same vertebrae, with the ten in the
above-mentioned Labrador duck. In the Call-duck, which had small ribs
attached to the fifteenth cervical vertebra, the haemal spines of the
thirteenth and fourteenth (cervical) and of the seventeenth (dorsal)
vertebrae corresponded with the spines on the fourteenth, fifteenth, and
eighteenth vertebrae of the wild duck: so that each of these vertebrae
had acquired a structure proper to one posterior to it in position. In
the twelfth cervical vertebra of this same Call-duck (fig. 40, B), the
two branches of the haemal spine stand much closer together than in the
wild duck (A), and the descending haemal processes are much shortened.
In the Penguin duck the neck from its thinness and erectness falsely
appears (as ascertained by measurement) to be much elongated, but the
cervical and dorsal vertebrae present no difference; the posterior
dorsal vertebrae, however, are more completely anchylosed to {284} the
pelvis than in the wild duck. The Aylesbury duck has fifteen cervical
and ten dorsal vertebrae furnished with ribs, but the same number of
lumbar, sacral, and caudal vertebrae, as far as could be traced, as in
the wild duck. The cervical vertebrae in this same duck (fig. 40, D)
were much broader and thicker relatively to their length than in the
wild (C); so much so, that I have thought it worth while to give a
sketch of the eighth cervical vertebra in these two birds. From the
foregoing statements we see that the fifteenth cervical vertebra
occasionally becomes modified into a dorsal vertebra, and when this
occurs all the adjoining vertebrae are modified. We also see that an
additional dorsal vertebra bearing a rib is occasionally developed, the
number of the cervical and lumbar vertebrae apparently remaining the
same as usual.

I examined the bony enlargement of the trachea in the males of the
Penguin, Call, Hook-billed, Labrador, and Aylesbury breeds; and in all
it was identical in shape.

The _Pelvis_ is remarkably uniform; but in the skeleton of the
Hook-billed duck the anterior part is much bowed inwards; in the
Aylesbury and some other breeds the ischiadic foramen is less
elongated. In the sternum, furcula, coracoids, and scapula, the
differences are so s