he lower extremity
(sciatic) in sitting upon a hard bench. The foot is then said to be
"asleep."

4th. When the trunk of a nerve is diseased or injured, the pain is
experienced in the outer extremity of the nerve. A blow upon the
elbow, which causes a peculiar sensation in the little finger and one
side of the ring finger, affords a familiar illustration. This
sensation is produced by injuring the ulnar nerve, which is
distributed to the little finger.

782. 3d. _Nerves of motion._ These are the third, sixth, and twelfth
pairs of cranial nerves, and the thirty-one pairs of spinal nerves.
These nerves are distributed to the fibres of the five hundred muscles
of the body. The functions of the muscular are different from those of
the sensitive nerves. The former are provided for the purpose of
motion, and not of feeling. Hence, muscles may be cut, and the pain
will be slight, compared with the cutting of the skin. This may be
called muscular pain. Weariness is a sensation recognized by one set
of muscular nerves.

783. So uniformly is a separate instrument provided for every
additional function, that there is strong reason to regard the
muscular nerves, although running in one sheath, as in reality double,
and performing distinct functions. Sir Charles Bell, in his work on
the Nervous System, endeavors to show, that one set of nervous fibres
conveys the mandate from the brain to the muscle, and excites the
contraction; and that another set conveys, from the muscle to the
brain, a peculiar sense of the state or degree of contraction of the
muscle, by which we are enabled to judge of the amount of stimulus
necessary to accomplish the end desired. This is obviously an
indispensable piece of information to the mind in regulating the
movements of the body.

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How is the peculiar sensation accounted for when we hear the grating
of a file or saw? What produces the sensation when the foot is said to
be "asleep?" What is the effect when the ulnar nerve is injured by a
blow? 782. Give the nerves of motion. What is said of the functions of
the muscular nerves? 783. What does Sir Charles Bell endeavor to
show?

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784. 4th. _Nerves of respiration._ These are the fourth, seventh,
ninth, tenth, and eleventh pair of cranial nerves, also the phrenic
and the external respiratory nerve. All of these nerves have their
origin in a distinct tract or column, called the lateral, in th