urved lower
jaws. In the skull the nasal and premaxillary bones are much shortened, the
maxillaries are excluded from any junction with the nasals, and all the
bones are slightly modified, even to the plane of the occiput. From the
analogical case of the dog, hereafter to be given, it is probable that the
shortening of the nasal and adjoining bones is the proximate cause of the
other modifications in the skull, including the upward curvature of the
lower jaw, though we cannot follow out the steps by which these changes
have been effected.

Polish fowls have a large tuft of feathers on their heads; and their skulls
are perforated by numerous holes, so that a pin can be driven into the
brain without touching any bone. That this deficiency of bone is in some
way connected with the tuft of feathers is clear from tufted ducks and
geese likewise having {333} perforated skulls. The case would probably be
considered by some authors as one of balancement or compensation. In the
chapter on Fowls, I have shown that with Polish fowls the tuft of feathers
was probably at first small; by continued selection it became larger, and
then rested on a fleshy or fibrous mass; and finally, as it became still
larger, the skull itself became more and more protuberant until it acquired
its present extraordinary structure. Through correlation with the
protuberance of the skull, the shape and even the relative connexion of the
premaxillary and nasal bones, the shape of the orifice of the nostrils, the
breadth of the frontal bone, the shape of the post-lateral processes of the
frontal and squamosal bones, and the direction of the bony cavity of the
ear, have all been modified. The internal configuration of the skull and
the whole shape of the brain have likewise been altered in a truly
marvellous manner.

After this case of the Polish fowl it would be superfluous to do more than
refer to the details previously given on the manner in which the changed
form of the comb, in various breeds of the fowl, has affected the skull,
causing by correlation crests, protuberances, and depressions on its
surface.

With our cattle and sheep the horns stand in close connexion with the size
of the skull, and with the shape of the frontal bones; thus Cline[834]
found that the skull of a horned ram weighed five times as much as that of
a hornless ram of the same age. When cattle become hornless, the frontal
bones are "materially diminished in breadth towards the po