Categories: THE SPEECH ORGANS
Sources: A Handbook Of Health
The Sixth Sense. Though we usually speak of having five
senses,--sight, smell, hearing, touch, and taste,--we really have also a
sixth--the sense of direction, or of balance. The machine of this
sense is comparatively simple, being made up of three tiny curved tubes,
which, from their shape, are called the semi-circular canals. These
are buried in the same bone of the skull as the internal ear, and
so close to it that they were at one time described as part of it.
These little canals are three in number, one for each of the
dimensions--length, breadth, and thickness,--so that whichever way the
head or body is moved,--backward and forward, up and down, or from side
to side,--the fluid with which they are filled will change its level in
one of them, just as the bead does in the carpenter's spirit-level
that you can find in any tool shop. The delicate nerve twigs that run
out into the fluid in these tiny canals are gathered together into a
bundle, or nerve-cable, which runs back to the part of the brain known
as the cerebellum or hind-brain, which has most to do with controlling
the balance and movements of our bodies.
It is the disturbance set up in these spirit-level canals by the
pitching and rolling of a ship, which makes us seasick. Neither the
stomach, nor anything that we may have eaten, has anything to do with
it. In the same way we sometimes become sick and dizzy from swinging too
long or too high, or from riding on the cars.