of selection, we ought not to expect to find great and constant differences in the skeleton; for fanciers can neither see, nor do they care for, modifications of structure in the internal framework. Nor ought we to expect changes in the skeletons from hanged habits of life; as every facility is given to the most distinct breeds to follow the same habits, and the much modified races are never allowed to wander abroad and procure their own food in various ways. Moreover, I find, on comparing the skeletons of Columba livia, œnas, palumbus, and turtur, which are ranked by all systematists in two or three distinct though allied genera, that the differences are extremely slight, certainly less than between the skeletons of some of the most distinct domestic breeds. How far the skeleton of the wild rock-pigeon is constant I have no means of judging, as I have examined only two.
Skull.—The individual bones, especially those at the base, do not differ in shape. But the whole skull, in its proportions, outline, and relative direction of the bones, differs greatly in some of the breeds, as may be seen by comparing the figures of (A) the wild rock-pigeon, (B) the shortfaced tumbler, (C) the English carrier, and (D) the Bagadotten carrier (of Neumeister), all drawn of the natural size and viewed laterally. In the carrier, besides the elongation of the bones of the face, the space between the orbits is proportionally a little narrower than in the rock-pigeon. In the Bagadotten the upper mandible is remarkably arched, and the premaxillary bones are proportionally broader. In the short-faced tumbler the skull is more globular; all the bones of the face are much shortened, and the front of the skull and descending nasal bones are almost perpendicular; the maxillo-jugal arch and premaxillary bones form an almost straight line; the space between the prominent edges of the eye-orbits is depressed. In the barb the premaxillary bones are much shortened, and their anterior portion is thicker than in the rock-pigeon, as is the lower part of the nasal bone. In two nuns the ascending branches of the premaxillaries, near their tips, were somewhat attenuated, and in these birds, as well as in some others, for instance in the spot, the occipital crest over the foramen was considerably more prominent than in the rock-pigeon.
Fig. 25.—Lower jaws, seen from above, of natural size. A. Rock-pigeon. B. Runt. C. Barb.
Fig. 26.—Skull of Runt, seen from above, of natural size, showing the reflexed margin of the distal portion of the lower jaw.
In the lower jaw, the articular surface is proportionally smaller in many breeds than in the rock-pigeon; and the vertical diameter more especially of the outer part of the articular surface is considerably shorter. May not this be accounted for by the lessened use of the jaws, owing to nutritious food having been given during a long period to all highly improved pigeons? In runts, carriers, and barbs (and in a lesser degree in several breeds), the whole side of the jaw near the articular end is bent inwards in a highly remarkable manner; and the superior margin of the ramus, beyond the middle, is reflexed in an equally remarkable manner, as may be seen in the accompanying figures, in comparison with the jaw of the rock-pigeon. This reflexion of the upper margin of the lower jaw is plainly connected with the singularly wide gape of the mouth, as has been described in runts, carriers, and barbs. The reflexion is well shown in fig. 26 of the head of a runt seen from above; here a wide open space may be observed on each side, between the edges of the lower jaw and of the premaxillary bones. In the rock-pigeon, and in several domestic breeds, the edges of the lower jaw on each side come close up to the premaxillary bones, so that no open space is left. The degree of downward curvature of the distal half of the lower jaw also differs to an extraordinary degree in some breeds, as may be seen in the drawings (fig. A) of the rock-pigeon, (B) of the short-faced tumbler, and (C) of the Bagadotten carrier of Neumeister. In some runts the symphysis of the lower jaw is remarkably solid. No one would readily have believed that jaws differing so greatly in the several above-specified points could have belonged to the same species.
Fig. 27.—Lateral view of jaws, of natural size. A. Rock-pigeon. B. Short-faced Tumbler. C. Bagadotten Carrier.
Vertebræ.— All the breeds have twelve cervical vertebræ.[[310]] But in a Bussorah carrier from India, the twelfth vertebra carried a small rib, a quarter of an inch in length, with a perfect double articulation.
The dorsal vertebræ are always eight. In the rock-pigeon all eight bear ribs; the eighth rib being very thin, and the seventh having no process. In pouters all the ribs are extremely broad, and, in three out of four skeletons examined by me, the eighth rib was twice or even thrice as broad as in the rock-pigeon; and the seventh pair had distinct processes. In many breeds there are only seven ribs, as in seven out of eight skeletons of various tumblers, and in several skeletons of fantails, turbits, and nuns. In all these breeds the seventh pair was very small, and was destitute of processes, in which respect it differed from the same rib in the rock-pigeon. In one tumbler, and in the Bussorah carrier, even the sixth pair had no process. The hypapophysis of the second dorsal vertebra varies much in development; being sometimes (as in several, but not all tumblers) nearly as prominent as that of the third dorsal vertebra; and the two hypapophyses together tend to form an ossified arch. The development of the arch, formed by the hypapophyses of the third and fourth dorsal vertebræ, also varies considerably, as does the size of the hypapophysis of the fifth vertebra.
The rock-pigeon has twelve sacral vertebræ; but these vary in number, relative size, and distinctness in the different breeds. In pouters, with their elongated bodies, there are thirteen or even fourteen, and, as we shall immediately see, an additional number of caudal vertebræ. In runts and carriers there is generally the proper number, namely twelve; but in one runt, and in the Bussorah carrier, there were only eleven. In tumblers there are either eleven, twelve, or thirteen sacral vertebræ.
The caudal vertebræ are seven in number in the rock-pigeon. In fantails, which have their tails so largely developed, there are either eight or nine, and apparently in one case ten, and they are a little longer than in the rock-pigeon, and their shape varies considerably. Pouters, also, have eight or nine caudal vertebræ. I have seen eight in a nun and jacobin. Tumblers, though such small birds, always have the normal number seven; as have carriers, with one exception, in which there were only six.
The following table will serve as a summary, and will show the most remarkable deviations in the number of the vertebræ and ribs which I have observed:—