The sympathetic system of mammals is centralized in a pair of ganglion-bearing, longitudinal sympathetic trunks, one on each side of the vertebral column. This trunk connects with the spinal cord through the spinal nerves, and also sends fibers to sympathetic plexuses in various parts of the body. These plexuses in turn send nerves to the viscera. Locate the two longitudinal sympathetic trunks in the rat, one on each side of the vertebral column. Trace one of these anteriorly to the head and posteriorly to the pelvic region. The superior cervical ganglion is a spindle-shaped enlargement near the bifurcation of the common carotid artery. The cervical portion of the trunk is dorsal to the tenth cranial nerve. The inferior cervical ganglion is the swelling of the trunk at the base of the neck. The thoracic section lies ventral to the ribs and presents ganglionic enlargements. The lumbar portion is median to the dorsal muscle mass in the lumbar region. Locate if possible the splanchnic nerves, which leave the thoracic ganglia in the vicinity of the eleventh and twelfth ribs, enter the abdomen, and go to the solar plexus. Find other rami of the sympathetic trunk.
THE SPINAL NERVES
The study of the spinal cord and the spinal nerves leading from it should be postponed until dissections and drawings of all other parts of the body, including the sympathetic system, have been completed. Expose the spinal nerves by carefully dissecting away the muscles ventral and lateral to the backbone, from the occipital region of the head to the base of the tail. The spinal nerves are designated according to the region in which they are found, cervical, thoracic, lumbar, sacral, and coccygeal.
The cervical spinal nerves, eight pairs in all, are in the neck. The first pair leaves the spinal canal through a fora-
