.--Lower jaws, seen from above, of natural size. A.
Rock-pigeon. B. Runt. C. Barb.]

[Illustration: 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 {165} 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.

[Illustration: Fig. 27.--Lateral view of jaws, of natural size. A.
Rock-pigeon. B. Short-faced Tumbler. C. Bagadotten Carrier.]

_Vertebrae._-- All the breeds have twelve cervical vertebrae.[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 v