THE CEPHALIC PORTION OF THE SYMPATHETIC SYSTEM 977 



Each spinal nerve receives a gray ramus commimicans from the sympathetic 

 trunk, but white rami are not supplied by all the spinal nerves. White rami are 

 derived from the first thoracic to the first lumbar nerves inclusive, while the 

 visceral branches which run from the second, third, and fourth sacral nerves directly 

 to the pelvic plexuses of the sympathetic belong to this category. The fibers which 

 reach the sympathetic through the white rami communicantes are medullated; 

 those which spring from the cells of the sympathetic ganglia are almost entirely 

 non-medullated. The sympathetic nerves consist of efferent and afferent fibers, the 

 origin and course of which are described on page 920) . 



The three great gangliated plexuses (collateral ganglia) are situated in front of 

 the vertebral column in the thoracic, abdominal, and pelvic regions, and are named, 

 respectively, the cardiac, the solar or epigastric, and the hypogastric plexuses. 

 They consist of collections of nerves and ganglia; the nerves being derived from 

 the sympathetic trunks and from the cerebrospinal nerves. They distribute 

 branches to the viscera. 



Development. The ganglion cells of the sympathetic system are derived from 

 the cells of the neural crests. As these crests move forward along the sides of the 

 neural tube and become segmented off to form the spinal ganglia, certain cells 

 detach themselves from the ventral margins of the crests and migrate toward the 

 sides of the aorta, where some of them are grouped to form the ganglia of the 

 sympathetic trunks, while others undergo a further migration and form the ganglia 

 of the pre vertebral and visceral plexuses. The ciliary, sphenopalatine, otic, and 

 submaxillary ganglia which are found on the branches of the trigeminal nerve are 

 formed by groups of cells which have migrated from the part of the neural crest 

 which gives rise to the semilunar ganglion. Some of the cells of the ciliary ganglion 

 are said to migrate from the neural tube along the oculomotor nerve. 



THE CEPHALIC PORTION OF THE SYMPATHETIC SYSTEM (PARS 

 CEPHALICA S. SYMPATfflCI). 



The cephalic portion of the sympathetic system begins as the internal carotid 

 nerve, which appears to be a direct prolongation of the superior cervical ganglion. 

 It is soft in texture, and of a reddish color. It ascends by the side of the internal 

 carotid artery, and, entering the carotid canal in the temporal bone, divides into 

 two branches, which lie one on the lateral and the other on the medial side of that 

 vessel. 



The lateral branch, the larger of the two, distributes filaments to the internal 

 carotid artery, and forms the internal carotid plexus. 



The medial branch also distributes filaments to the internal carotid artery, and, 

 continuing onward, forms the cavernous plexus. 



The internal carotid plexus (plexus caroticus internus; carotid plexus} is situated 

 on the lateral side of the internal carotid artery, and in the plexus there occasionally 

 exists a small gangliform swelling, the carotid ganglion, on the under surface of 

 the artery. The internal carotid plexus communicates with the semilunar gan- 

 glion, the abducent nerve, and the sphenopalatine ganglion; it distributes filaments 

 to the wall of the carotid artery, and also communicates with the tympanic branch 

 of the glossopharyngeal nerve. 



The communicating branches with the abducent nerve consist of one or two 

 filaments which join that nerve as it lies upon the lateral side of the internal carotid 

 artery. The communication with the sphenopalatine ganglion is effected by a 

 branch, the deep petrosal, given off from the plexus on the lateral side of the artery; 

 this branch passes through the cartilage filling up the foramen lacerum, and joins 

 the greater superficial petrosal to form the nerve of the pterygoid canal (Vidian 

 nerve), which passes through the pterygoid canal to the sphenopalatine ganglion. 

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