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

ANATOMY OF NERVES. 25
the case I have just mentioned is a fair illustration, although
few surgeons are without similar experiences.
Besides this insurance against certain forms of disease,
the structure of the nerve fibre, and its vascular relationships,
also contribute to its safety, for as each nerve fibre
has its sheath, the essential axis cylinder is well protected;
while also the absence, in man at least, of blood-vessels
within the delicate covering described by Robin, serves
to prevent, to some extent, the access of inflammation.
Thus it is that the nerves are able to traverse, uninjured,
parts in divers states of degeneration or inflammation.
It is also this sheathing by a non-vascular envelope that
limits to a degree the changes caused by neuritis, and
enables the non-vascular fibres to recover rapidl}'
and thoroughly
from such disease, because during inflammation
the nerve fibres sufi'er principally from pressure, owing to
effusion in and about the vascular portions of the nerve.
The toughness and general elasticity of nerve trunks
sometimes serve a useful purpose in cases of ball wound,
and I have repeatedly seen nerves escape total destruction
from missiles simply because they were thrust aside, instead
of being divided. Some of these escapes, which can
be explained in no other way, are very interesting.
They
are most apt to occur where a missile has passed through
a limb midway between two joints. On the other hand,
of nerves in connection with bone or near to
injuries
joints are likely to be severe and lasting, because at these
points and in these positions the nerve trunk is more
firmly anchored than elsewhere, and shares in every injury
which directly affects parts in its near neighborhood.
When a spinal nerve emerges from the intervertebral
canal it is motor and sensory, by the union of the anterior
and posterior roots, which represent motion and sensation
respectively. Whether or not these fibres become
at once scattered so that every part of the area of the
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