(cerebro-spinal axis), there is, on either side of the dorsal wall of the
body cavity, a sympathetic nervous chain. The nerve fibres of this
system, like the nerve fibres of invertebrates, are non-medullated. It
may be seen as a greyish thread running close by the common
carotid in the neck (sym., Figure 1); it then runs over the heads of
the ribs in the thorax and close beside the dorsal aorta in the
abdominal region. In the anterior region of the neck it dilates to form
a superior cervical ganglion, and opposite the first rib it forms an
inferior cervical ganglion. Thence, backwards, there is a ganglion on
each sympathetic chain opposite each spinal nerve, and the two
exchange fibres through a thread, the ramus communicans. To the
sympathetic chain is delegated much of the routine work of reflex
control of the bloodvessels and other viscera, which would otherwise
fall upon the spinal cord.