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

28 INJURIES OF NERVES.
reptiles and birds. He has also discovered that in frogs
the uerves of the skin cross the central line of the body.
I have recently examined frogs to learn whether this
anatomical crossing involves physiological consequences.
To test this, the skin of the frog's back or belly was divided
longitudinally at varying distances from the middle
line, and then irritants, as biliary and stronger acids,
were applied to the skin between the central raphe and
the line of section; no response was obtained to such
irritations, even in frogs which had been previously rendered
excitable by strychnia. The purpose, therefore,
of such interchange of nerves must still be considered
doubtful.
During their distribution, the nerves from more or less
remote parts of the nervous system in some localities
run together, and then separate to reunite and part anew,
thus forming, by the free communication between neighboring
branches, a plexus or network, from which emerge
finally the nerve trunks which are to be distributed to a
particular member. This intricate interlacing seems to
be merely an arrangement for the interchange of fibres,
since those which enter the plexus acquire in it no physiological
properties which they did not previously possess.
A knowledge of these networks is essential to the studv
of nerve wounds, because injuries
of the plexuses, especially
that of the neck, are very common in war, and
their arrangements enable us to explain in many cases
the transmission of disease from one nerve to another,
which is closely related to it in the plexus, or as its
parent stem. After leaving the plexus, the limb nerves
are usually distributed with great regularity, anomalies
being rather uncommon.
While in most men we may take for granted that nerves
obey the normal law, it is still important to remember
that in the arm especially, peculiar and exceptional ar-