Branches of the Sympathetic in the Cervical Region.—From the cranial end of the superior cervical ganglion several nerves pass craniad. Some of these become connected immediately with the cranial nerves emerging from the jugular foramen, forming a plexus in this region. Others pass with the internal carotid artery craniad, forming a plexus about that artery; from the plexus twigs arise which pass to the fifth and sixth cranial nerves; doubtless also to the seventh and eighth. A specially large branch, the deep petrosal nerve (see [page 373]), passes from the superior cervical ganglion along with the internal carotid artery to the pterygoid canal, thence through this to the sphenopalatine ganglion. Before separating from the vagus the sympathetic gives off one or two cardiac nerves ([Fig. 157], i). These are closely bound up with the vagus (b), so that they appear usually to have origin from the vagus at about the level of the first rib. These pass with the vagus to the heart and take part in the formation of the cardiac plexus (k).
At the middle cervical ganglion (d) usually a communicating branch is given to the vagus. The branches of the inferior cervical ganglion (e) fall in the thoracic region, and are [described] in that connection.
Thoracic Portion of the Sympathetic ([Fig. 157], [page 381]).—The inferior cervical ganglion (e) lies entirely within the thoracic cavity. It has the following branches:
1. One or two small cardiac branches (h), which pass to the heart (r).
2. A large communicating branch (e′), which passes craniad from the cranial end of the ganglion (e) along the lateral surface of the longus colli muscle, and gives communicating branches to the sixth, seventh, and eighth cervical nerves (VI, VII, and VIII).
3. One or two small communicating branches to the first thoracic nerve (I′).
4. A communicating branch to the second thoracic nerve.
The arrangement of these communicating branches is somewhat variable; they may arise in various combinations, as at first united, or as more or less completely separated nerves.
The sympathetic trunk (c) continues caudad from the caudal end of the inferior cervical ganglion, lying at first on the lateral surface of the longus colli, then on the lateral surface of the centra of the vertebræ. For each vertebra there is a slight enlargement, forming one of the thoracic ganglia of the sympathetic, and from each ganglion one or two communicating branches are given off to the corresponding spinal nerve. Just caudad of the last rib (but while still in the thoracic cavity) the sympathetic gives off the large N. splanchnicus major or great splanchnic nerve (n), which passes ventrocaudad and pierces the diaphragm. The sympathetic itself then passes through the diaphragm laterad of the crus.
Abdominal Portion of the Sympathetic ([Fig. 164]).—The great splanchnic nerve (b) passes through the diaphragm (2) laterad of the crus, extends two or three centimeters caudoventrad, and joins a large ganglion lying just caudad of the cœliac artery (4), almost on the lateral surface of the superior mesenteric (5). This is the cœliac (or semilunar) ganglion (d). From it nerves branch in all directions, forming the cœliac plexus (c), a part of the large solar plexus. Less than a centimeter ventrocaudad of the cœliac ganglion, on the caudal surface of the superior mesenteric artery (5), is the somewhat smaller superior mesenteric ganglion (f); the two are connected by two strong nerve-trunks.