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

ANATOMY OF NERVES. 15
which, running in every direction, and crossing each other
at all
imaginable angles, leave between them minute
areolee of irregular form. Within, upon, and about the
fibrous sheath, a considerable amount of fine adipose tissue
exists in the primarj^, and even in the secondary, divisions
of the nerve. It is met with in the most emaciated,
and follows chiefly the track of the neural blood-vessels,
or is found collected here and there in small masses.
Contrary to the common opinion, Sappeyhas found that
the vascularity of the nerve sheaths is greater than that of
ligaments, tendons, or aponeuroses, and approaches in this
respect the spinal or cerebral pia mater.
The arteries are exceedingly numerous, and lie chiefly
between the walls of the fibrous partitions in the spaces
formed by their juxtaposition. The veins, sometimes
single, at others double, form, like the arteries, an intricate
plexus, but neither are met with in the sheath of the
ultimate nerve fibre.
The nerve sheaths also possess nerves which follow the
path of the vessels, and are less and less numerous as the
nerve branches, until, on the smaller divisions, they are
said to be absent. Sappey has described them as nervi
nervorum, a phrase to which there is no objection, unless
we attribute to the words too large a physiological significance,
since, in reality, these fibres are rather nerves of
the sheath than of the nerves themselves. They in all
respects resemble other neural fibres, except that they are
unusually minute. Each nerve, as we follow it with the
naked eye, surrounded and protected by
its neurilemma
of connective tissue, is capable of being further resolved
by the microscope into rodlets or fasciculi, known as the
fibres or tubules. Around each collection of
primitive
these is the delicate sheath which Robin has admirably
described as the perineurium. The structure of this covering
is very simple. It is
composed of an almost homo-