an the same rock-pigeon,
the furcula was a quarter of an inch shorter. In a pouter, the furcula
had not been lengthened proportionally with the increased length of the
body. In a short-faced tumbler, which measured from tip to tip of wings
24 inches, therefore only 21/2 inches less than the rock-pigeon, the
furcula was barely two-thirds of the length of that of the rock-pigeon.

We thus clearly see that the sternum, scapulae, and furcula are all reduced
in proportional length; but when we turn to the wings we find what at first
appears a wholly different and unexpected result. I may here remark that I
have not picked out specimens, but have used every measurement made by me.
Taking the length from the base of beak to the end of the tail as the
standard of comparison, I find that, out of thirty-five birds of various
breeds, twenty-five have wings of greater, and ten have them of less
proportional length, than in the rock-pigeon. But from the frequently
correlated length of the tail and wing-feathers, it is better to take as
the standard {176} of comparison the length from the base of the beak to
the oil-gland; and by this standard, out of twenty-six of the same birds
which had been thus measured, twenty-one had wings too long, and only five
had them too short. In the twenty-one birds the wings exceeded in length
those of the rock-pigeon, on an average, by 1-1/3 inch; whilst in the five
birds they were less in length by only .8 of an inch. As I was much
surprised that the wings of closely confined birds should thus so
frequently have been increased in length, it occurred to me that it might
be solely due to the greater length of the wing-feathers; for this
certainly is the case with the jacobin, which has wings of unusual length.
As in almost every case I had measured the folded wings, I subtracted the
length of this terminal part from that of the expanded wings, and thus I
obtained, with a moderate degree of accuracy, the length of the wings from
the ends of the two radii, answering from wrist to wrist in our arms. The
wings, thus measured in the same twenty-five birds, now gave a widely
different result; for they were proportionally with those of the
rock-pigeon too short in seventeen birds, and in only eight too long. Of
these eight birds, five were long-beaked,[313] and this fact perhaps
indicates that there is some correlation between the length of the beak and
the length of the bones of the wings,