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220 THE NERVES AND THE BRAIN.
56. THE NERVES AND THE BRAIN.
1. Have you ever looked carefully at a rabbit when
your mother has got one in from the butcher for your
dinner? If so, you may have notice that, when the
skin is removed, the red muscles can be easily seen
on the body and limbs of th e animal. If you separate
carefully the muscl es that lie along the back
of the hind leg, you will see a little white thread
running down the leg. This is a nerve, the largest
nerve in the whole body, and it is known as the
sciat ic nerve. We have a similar nerve in our bodies ;
and when it becomes inflamed, it causes the painful
disease called sciatica.
2. If you follow this nerve down the rabbit's leg, it
will be seen to branch again and I1gain, same or the
tittle tw igs passing to the skin, and others to the
muscles of th e limb. If you trace the nerve upwards
into the body, which is not so easy, it will be seen to
pass into the backbone. Th e backbone consists of a
string of bones forming 11 hollow tube, which is filled
with 11 long cord of soft white material. In the
head this cord expands into the brain. A great many
other nerves leav e the spinal cord on both sides and
pass to the body and the limbs, and some twenty
more pass from the brain to the head and such parts
as the eyes, the nose, and the ears.
3. Small as these nerves are-some of them thinner
than the thinnest thread-the microscope shows that
each of th em is composed of hundreds, sometimes
thousands, of microscopic threads closely packed side
by side, and bound together by material of very great
delicacy. The nerves, then, form a system of cords