Injuries of nerves and their consequences - Reflex Sympathetic ...

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22 INJURIES OF NERVES.
the terminal nerve fibre of motor nerves does not perforate
this sarcolemma, but forms a network on its surface.
This view, Kiihne contends, is due to imperfect observation,
though we confess that Dr. Beale's drawings,
if correct,
scarcely admit any other interpretation than that
which he places on them.
Before passing to the consideration of the laws which
control the passage of impressions over nerve fibres, there
are a few points to be considered which concern the general
or rational anatomj^ of nerves, and derive importance
from their connection with disease or wounds of these
parts.
Protection of nerves, owing to their physical peculiarities.—
The fibrous character of the grosser nerve sheath, and
the fact of each nerve being composed of a multitude
of fibres, give to the nerves far more strength or power
of resistance than might be supposed to belong to it,
if we considered only the delicate structure of the
neural substance itself
Dr. P. Tillaux* has examined this
sciatic nerves of
subject with the following results The :
two fresh bodies were laid bare at the level of the popliteal
space, then all the other parts of the member having
been cut across so that the limb remained attached to the
body by the nerve trunk alone, traction was made upon
the limb in the direction — of the nerve. A power equal to
54 to 58 kilogrammes 108 to 116 lbs.— was found to be
necessary in order to rupture the nerve. To break the
median or ulnar, under similar circumstances, a force of
40 to 50 lbs. was requisite. In practice
it has been observed
that when a limb is torn oft',
the nerve frequently gives
way at a point above that at which the other parts are
torn. Thus the sciatic
may be broken oft' at the level of the
buttocks, owing to the external and posterior portions of
* Tillaux, Aff. cMr. des Nerfs, p. 11.