see that there are conscious sensations of rotation
from the canals, and that these give information of the starting or
stopping of a rotation, though not of its steady continuance.
Excessive stimulation of the canals gives the sensation of dizziness.

The otolith organs in the vestibule are probably excited, not by
rotary movements, but by sudden startings and stoppings of rectilinear
motion, as in an elevator; and also by the pull of gravity when the
head is held in any position. They give information regarding the
position and rectilinear movements of the head, as the canals do of
rotary head movements. Both are important in maintaining equilibrium
and motor efficiency.

The muscle sense is another sense of bodily movement; it was the
"sixth sense", so bitterly fought in the middle of the last century by
those who maintained that the five senses that were enough for our
fathers ought to be enough for us, too. The question was whether the
sense of touch did not account for all sensations of bodily movement.
It was shown that there must be something besides the skin sense,
because weights were better distinguished when "hefted" in the hand
than when simply laid in the motionless palm; and it was shown that
loss of skin sensation in an arm or leg interfered much less with the
cooerdinated movements of the limb than did the loss of all the sensory
nerves to the limb.

[Illustration: Fig. 41.--(From Cajal.) A "tendon spindle," very
similar to the muscle spindle spoken of in the text, but found at
the tendinous end of a muscle instead of embedded in the muscle
substance itself, "a" indicates the tendon, and "e" the muscle
fibers; "b" is a sensory axon, and "c" its end-brush about the
spindle. Let the tendon become taut in muscular contraction, and the
fine branches of the sensory axon will be squeezed and so
stimulated.]

Later, the crucial fact was established {239} that sense organs (the
"muscle spindles") existed in the muscles and were connected with
sensory nerve fibers; and that other sense organs existed in the
tendons and about {240} the joints. This sense accordingly might
better be called the "muscle, tendon and joint sense", but the shorter
term, "muscle sense", bids fair to stick. The Greek derivative,
"kinesthesis", meaning "sense of movement", is sometimes used as an
equivalent; and the corresponding adjective, "kinesthetic", is common.

The muscle sense informs us of movements of th