tissues. The nerve fibres there figured are bound together by
endoneurium into small ropes, the nerves, encased in perineurium.
There is always a grey axis cylinder (a.c.), which may (in medullated
nerves), or may not (in non-medullated or grey nerves) have a
medullary sheath (s.S.) interrupted at intervals by the nodes of
Ranvier (n.R.). Nuclei (n.) at intervals under the sheath indicate the
cells from which nerve fibres are derived by a process of elongation.
The nerves of invertebrata, where they possess nerves, are mostly
grey, and so are those of the sympathetic system of vertebrata, to
be presently described, g.c., g.c. are ganglion cells; they may have
many hair-like processes, usually running into continuity with
the axis cylinders of nerve fibres, in which case they are called
multi-polar cells, or they may be uni- or bi-polar.