in the same manner as with the feet
and tarsi. The shortening of the humerus and radius in the seventeen birds
may probably be attributed to disuse, as in the case of the scapulae and
furcula to which the wing-bones are attached;--the lengthening of the
wing-feathers, and consequently the expansion of the wings from tip to tip,
being, on the other hand, as completely independent of use and disuse as is
the growth of the hair or wool on our long-haired dogs or long-woolled
sheep.

To sum up: we may confidently admit that the length of the sternum, and
frequently the prominence of its crest, the length of the scapulae and
furcula, have all been reduced in size in comparison with the same parts in
the rock-pigeon. And I {177} presume that this may be safely attributed to
disuse or lessened exercise. The wings, as measured from the ends of the
radii, have likewise been generally reduced in length; but, owing to the
increased growth of the wing-feathers, the wings, from tip to tip, are
commonly longer than in the rock-pigeon. The feet, as well as the tarsi
conjointly with the middle toe, have likewise in most cases become reduced;
and this it is probable has been caused by their lessened use; but the
existence of some sort of correlation between the feet and beak is shown
more plainly than the effects of disuse. We have also some faint indication
of a similar correlation between the main bones of the wing and the beak.

_Summary on the Points of Difference between the several Domestic Races,
and between the individual Birds._--The beak, together with the bones of
the face, differ remarkably in length, breadth, shape, and curvature. The
skull differs in shape, and greatly in the angle formed by the union of the
premaxillary, nasal, and maxillo-jugal bones. The curvature of the lower
jaw and the reflexion of its upper margin, as well as the gape of the
mouth, differ in a highly remarkable manner. The tongue varies much in
length, both independently and in correlation with the length of the beak.
The development of the naked, wattled skin over the nostrils and round the
eyes varies in an extreme degree. The eyelids and the external orifices of
the nostrils vary in length, and are to a certain extent correlated with
the degree of development of the wattle. The size and form of the
oesophagus and crop, and their capacity for inflation, differ immensely.
The length of the neck varies. With the varying shape of the body, the
breadt