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

14 INJURIES OF NERVES.
ganglion and both sets of fibres on coming together constitute
one spinal nerve. The anterior root is motor in
;
function; the posterior, sensory: the former carries messages
from, and the latter to, the nerve centres. Thus
constituted, the compound nerve passes outward until
its fibres, separating anew into their phj-siological constituents,
enter the muscles on the one part, or are
distributed to the surfaces upon the other.
The nerve so made up has, at an early part of its course,
certain relations to the chain of sympathetic ganglia, with
which there is
probably a mutual interchange of filaments.
Besides the various fibres devoted to forms of sensation
and to motion, whether vasal or muscular, each nerve
is
by some authors supposed to possess nutritive or trophic
filaments, which may be derived either from the spinal
centres or from the sympathetic system,
— a point as yet
undetermined.
The trunk of each of the spinal nerves is surrounded
by a neurilemma, or general sheath, which has the same
relation to the nerves as the myolemma has to the muscles.
It has been best described by Robin, in 1854, and
still further by Sappey,* in 1868. This sheath surrounds
the nerve at its escape from the cord, sends out prolongations
which pass in between the separate bundles and
fibres, and dividing and subdividing, as the branches become
smaller, follows them through their multiplied
divisions until it envelops with a delicate membrane the
primitive fibres themselves, and is lost to view just before
these end in the muscles or the sensitive surfaces. The
portion which covers the ultimate tubules has certain
peculiarities of structure to which I shall presently refer.
The sheath of the main nerve trunk, and of its lesser
divisions, is composed of fibrous tissue,
the strands of
* Journ. de I'Anat. et de Phys., 1868, t. V. p. 48.