133). Two deep fissures, one in front
and the other at the back, extend the entire length of the cord, and
separate it into two similar divisions. These are connected, however,
along their entire length by a central band consisting of both gray and
white matter.
[Fig. 133]
Fig. 133--*Spinal cord*, showing on one side the nerves and ganglia with
which it is closely related in function. _A._ Bulb. _B._ Cervical
enlargement. _C._ Lumbar enlargement. _D._ Termination of cord. _E._ Nerve
roots that occupy the spinal cavity below the cord. _P._ Pons. _D.G._
Dorsal root ganglia. _S.G._ Sympathetic ganglia. _N._ Nerve trunks to
upper and lower extremities.
The arrangement of the neurons of the spinal cord is just the reverse of
that in the cerebrum--the center being occupied by a double column of
cell-bodies, which give it a grayish appearance, while the fibers occupy
the outer portion of the cord, giving it a whitish appearance.
The spinal cord is not uniform in thickness, but tapers slightly, though
not uniformly, from the upper toward the lower end. At the places where
the nerves from the arms and legs enter the cord two enlargements are to
be found, the upper being called the _cervical_ and the lower the _lumbar
enlargement_.
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