548 THE NERVOUS SYSTEM 



numerous gray nerve strands. These are all composed of postganglionic fibers 

 which arise in this ganglion. They run to the neighboring cranial and spinal 

 nerves, to which they carry vasomotor, pilomotor, and secretory fibers, and to the 

 heart, pharynx, and the internal and external carotid arteries (Figs. 248, 250, 

 257). The most important of these branches of the superior cervical ganglion 

 are the three following: (1) The superior cervical cardiac nerve, which runs 

 from the superior cervical ganglion to the cardiac plexus, carries accelerator 

 fibers to the heart. (2) The internal carotid nerve runs vertically from the 

 ganglion to the internal carotid artery, about which its fibers form a plexus, 

 known as the internal carotid plexus (Fig. 257). It is by way of this nerve and 

 plexus that the pupillary dilator fibers reach the eye (Fig. 247). (3) The branch 

 of the superior cervical ganglion to the external carotid artery breaks up into a 

 plexus on that artery. A continuation of this plexus extends along the external 

 maxillary artery, and carries secretory fibers to the submaxillary salivary gland. 



The middle and inferior cervical sympathetic ganglia are smaller. Among 

 the branches from these ganglia we may mention the gray rami to the adjacent 

 spinal nerves and the middle and inferior cardiac nerves to the cardiac plexus 

 (Figs. 248, 257). 



The thoracic portion of the sympathetic trunk is connected with the thoracic 

 nerves by the gray and white rami. In addition to the rami communicantes 

 and some small branches to the aortic and pulmonary plexuses, there are three 

 important branches of the thoracic portion of the sympathetic trunk known as 

 the splanchnic nerves. These run through the diaphragm for the innervation 

 of abdominal viscera (Figs. 248, 257). The greater splanchnic nerve is usually 

 formed by branches from the fifth to the ninth thoracic sympathetic ganglia 

 and after piercing the diaphragm joins the celiac ganglion. The smaller splanch- 

 nic nerve is usually formed by branches from the ninth and tenth thoracic 

 sympathetic ganglia and terminates in the celiac plexus. The lowermost splanch- 

 nic nerve arises from the last thoracic sympathetic ganglion and terminates in 

 the renal plexus. These splanchnic nerves, although they appear to be branches 

 of the thoracic sympathetic trunk, are at least in major part composed of fibers 

 from the white rami, which merely pass through the trunk on their way to the 

 ganglia of the celiac plexus (Figs. 250, 257; Langley, 1900; Ranson and Billings- 

 ley, 1918). 



THE SYMPATHETIC PLEXUSES 



The Sympathetic Plexuses of the Thorax. In close association with the 

 vagus nerve in the thorax are three important sympathetic plexuses. The 



