Section 133. There are eight cervical (spinal) nerves, one in front of

the atlas, and one behind each of the cervical vertebrae. The last four

and the first thoracic (spinal) contribute to a leash of nerves running

out to the fore limb, the brachial plexus (plexus, literally network, but

here meaning a plaited cord). The fourth cervical also sends down a

phrenic nerve (p.n., Figure 1), along by the external jugular vein and

the superior caval vein to the diaphragm. The last three lumbar and

the sacral nerves form a sacral plexus, supplying the hind limb.