n animal of nearly the same
{129} size,--I conclude, notwithstanding the remarkable differences in
capacity in the skulls of the small P. Santo rabbits, and likewise in the
large lop-eared kinds, that in all long-domesticated rabbits the brain has
either by no means increased in due proportion with the increased length of
the head and increased size of the body, or that it has actually decreased
in size, relatively to what would have occurred had these animals lived in
a state of nature. When we remember that rabbits, from having been
domesticated and closely confined during many generations, cannot have
exerted their intellect, instincts, senses, and voluntary movements, either
in escaping from various dangers or in searching for food, we may conclude
that their brains will have been feebly exercised, and consequently have
suffered in development. We thus see that the most important and
complicated organ in the whole organization is subject to the law of
decrease in size from disuse.

Finally, let us sum up the more important modifications which domestic
rabbits have undergone, together with their causes as far as we can
obscurely see them. By the supply of abundant and nutritious food, together
with little exercise, and by the continued selection of the heaviest
individuals, the weight of the larger breeds has been more than doubled.
The bones of the limbs have increased in weight (but the hind legs less
than the front legs), in due proportion with the increased weight of body;
but in length they have not increased in due proportion, and this may have
been caused by the want of proper exercise. With the increased size of the
body the third cervical vertebra has assumed characters proper to the
fourth cervical; and the eighth and ninth dorsal vertebrae have similarly
assumed characters proper to the tenth and posterior vertebrae. The skull in
the larger breeds has increased in length, but not in due proportion with
the increased length of body; the brain has not duly increased in
dimensions, or has even actually decreased, and consequently the bony case
for the brain has remained narrow, and by correlation has affected the
bones of the face and the entire length of the skull. The skull has thus
acquired its characteristic narrowness. From unknown causes the
supra-orbital processes of the frontal bones and the free end of the malar
bones have increased in breadth; and in the larger breeds {130} the
occipital foramen is g