Lying on the necks of the ribs, just lateral to their heads, and anterior to the intercostal vessels and nerves, is the thoracic part of the sympathetic trunk. It is described as possessing 12 ganglia, one for each intercostal nerve, but characteristically there are fewer, the result of fusion of adjacent ganglia. Thus the first ganglion is commonly fused with the inferior cervical ganglion to form the cervicothoracic (stellate) ganglion. It is simplest, however, to describe them as though they consisted of 12 discrete ganglia. Each receives a white ramus from its corresponding spinal nerve, and this emerges from the anterior ramus of the nerve. After relay in the ganglion a postganglionic gray ramus is given to each thoracic nerve, and this usually lies medial to the white ramus.
The heart is supplied with sympathetic fibers from the cervical and upper thoracic ganglia through the cardiac plexus. The pulmonary part supplies the lungs. The trachea and esophagus receives branches from trunk ganglia, but note that the esophageal plexus is a vagal plexus.
The splanchnic nerves, three in number, come from the lower eight ganglia. The lowest, or least splanchnic nerve leaves the twelfth ganglion; the lesser splanchnic nerve comes from the tenth and eleventh. The greater splanchnic nerve is formed by branches from the fifth to the ninth ganglia. Each pierces the crus of its own side to relay in the celiac ganglia.
The thoracic trunk is continued upwards over the neck of the first rib as the cervical sympathetic trunk. It crosses the neck of the first rib well on the medial side, near the head. The main part of the first thoracic nerve, passing out of the thorax into the neck to join the brachial plexus, crosses the neck of the first rib more laterally. Between the two at this level lie the supreme intercostal vein medially, and the superior intercostal artery laterally. Classical description of the ganglia consists of describing the first thoracic ganglion as lying below the neck of the first rib, and the inferior cervical ganglion lying in the root of the neck just above the neck of the rib, posteromedial to the vertebral artery. More often than not, however, these two ganglia are fused into a single mass, the cervicothoracic or stellate ganglion, overlying the neck of the first rib. It is very variable in size and may measure as 2 cm in length and 0.5 cm in diameter.
The thoracic trunk is continued downwards into the abdomen by passing behind the medial arcuate ligament of the diaphragm, lying on the front of the fascia on the upper part of psoas muscle.