224 The Spinal Cord 



the ganglion impar. From these knots, or ganglia, offshoots join the 

 spinal nerves, and branches pass off, frequently in intricate plexuses 

 along the neighbouring vessels. The chief office of the system is the 

 control of the non-striated muscular tissue of the blood-vessels, lym- 

 phatics, and hollow viscera, and it is through them that the calibre of 

 these vessels and viscera is regulated (asthma, p. 197). 



In the cervical region the knots are represented by three ganglia 

 which lie behind the carotid sheath, the superior ganglion being a long 

 fusiform mass opposite the second and third vertebrae. The middle 

 ganglion is at the level of the inferior thyroid artery, and the lowest 

 ganglion is near the neck of the first rib, whence it sends filaments 

 up with the vertebral artery. 



From the superior cervical ganglion filaments ascend into the skull 

 with the internal carotid artery, to form the cavernous and carotid 

 plexuses, from which branches pass along the ophthalmic and the 

 cerebral divisions of the artery. Other offshoots of the cervical 

 ganglia accompany the branches of the external carotid, certain twigs 

 join the pharyngeal plexus (p. 138), and some descend to the cardiac 

 plexuses. Communications also pass to the spinal nerves. 



The cardiac plexuses. The superficial plexus is below the arch 

 of the aorta, and receives branches from the cervical part of the left 

 vagus and sympathetic, and from the deep plexus. The deep plexus 

 receives a large number of branches from the gangliated cords, and 

 also from the vagi in the neck. From these plexuses networks extend 

 along the coronary arteries and into the pulmonary plexuses. 



In the thorax the sympathetic ganglia, lying near the heads of the 

 ribs, close behind the pleura, send branches to the dorsal nerves. 

 The upper six ganglia also give filaments to the thoracic aorta and to 

 the pulmonary plexus, and the lower six send down the splanchnic 

 (0-TrXuyxi/a, viscera} nerves to the viscera of the abdomen. 



The great splanchnic is formed of offsets from the sixth to the 

 tenth, and, descending through the crus of the diaphragm, ends in 

 the semilunar ganglion and in the renal and supra-renal plexus. 



The lesser splanchnic, from the tenth and eleventh, passes down to 

 the cceliac plexus, and the least splanchnic to the renal plexus. 



In the abdomen the four or five pairs of ganglia send branches on 

 to the front of the aorta, and others over the common iliac arteries 

 to form the hypogastric plexus. The solar plexus, part of the aortic 

 network, is between the crura and behind the stomach, and sends 

 filaments along the chief visceral branches of the abdominal aorta, 

 under the names of supra-renal, renal, spermatic, cceliac, and superior 

 mesenteric plexuses. The solar plexus contains several ganglia, of 

 which the semilunar receive the ending of the great splanchnic 

 nerves. 



The aortic plexus is that part of the network which sends off the 

 inferior mesenteric plexus ; it ends in the hypogastric plexus. 



