C H APTE R VIII. 
THE NERVOUS SYSTEM AND SPECIAL ORGANS. 
The nervous system. — The nervous system consists of [a) the 
brain, {h) the spinal cord, [c] the nerves. 
{^a) The brain is contained within the cranial cavity. It is 
^ the organ that regulates every vital process in the 
body ; it is the seat of the will and intelligence ; it 
controls all motion, appreciates and locates sensation, 
and its activity is exhibited in part by what is termed 
consciousness. 
\h) The spinal cord is contained within the vertebral canal, 
and is in relation to the brain what a local post office 
is to the general post office. It only controls certain 
functions of the body and even in those is itself 
controlled by the brain. 
[c) The nerves are merely conducting media between 
sensitive surfaces or organs and the brain and cord. 
They are the telegraph wires which convey the 
messages emanating from the brain or spinal cord, 
the outcome of which may be seen in a variety of 
ways, such as size of the pupil, degree of redness of 
mucous membranes, the activity in the secretion of a 
gland, the movement of a muscle or a limb, the voiding 
of excreta, etc. 
Eye. — The optic nerve is responsible for the sense of vision 
and is unusually small in the elephant, the reason for which is 
evident when one considers the small size of this organ and the 
muscles required to move it. The eye resembles that of other animals. 
The visible portion consists of a transparent convex disc like a 
watch glass called the cornea, behind which is the coloured portion 
of the eye (iris) w^hich is usually brown, and centrally the pupil 
which is jet black and round. Vision is acute, but the animal is 
greatly handicapped in making use of this sense to a degree equal 
to that of most animals by virtue of the shortness of its neck which 
will not permit of the head being turned sideways sufficiently to see 
objects in its rear : therefore the only way this can be effected is by 
a movement of the body, and this is exemplified by watching an 
elephant walking when it is suspicious of something in its rear. 
