NERVOUS TISSUE 139 



cous membrane, where they form another plexus (the plexus submu- 

 cosus). In this way the sympathetic system supplies the intestine. 

 It sends its fibers into other organs, following the arteries, thus forming 

 the hepatic, splenic, suprarenal and renal plexuses. In the pelvis the 

 sympathetic rami form the hypogastric plexus, with branches distributed 

 to the rectum, bladder and urogenital organs, and finally it accompanies 

 the arteries down the legs, innervating the muscles in the walls of the 

 vessels. 



In 1664, Willis published a remarkably clear account of the nerve "commonly 

 called intercostal because it rests against the roots of the ribs." This nerve, which is 

 the ganglionated trunk of the sympathetic system, had generally been supposed to 

 descend from the cerebral nerves. Willis described its connections with these nerves 

 and, through each intercostal space, with the spinal cord. He noted the cardiac 

 branches, and stated that the great mesenteric plexus, placed in the midst of the others, 

 like a sun, sent its nerve fibers like rays in all directions (hence it came to be called the 

 "solar plexus"). Willis found that this nerve sent branches to all the abdominal 

 organs below the stomach. He considered that its function was to place the heart 

 and viscera in connection with the brain so that they should act in harmony 

 (Anatome cerebri, Amstelodami, 1664). Because of their frequent communications 

 with other nerves, Winslow (1732) called the ganglionated trunks the Nervi sympa- 

 thetic? maximi. 



Bichat (Anatomic Gen6rale, 1802, translated by Hayward 1822) subdivided the 

 nervous system into two parts "essentially distinct from each other, the one having 

 the brain and its dependencies for its principal center, and the other having the gang- 

 lions." The latter is "almost everywhere distributed to the organs of digestion, 

 circulation, respiration, and secretion." "Each ganglion is a distinct center, inde- 

 pendent of the others in its action, furnishing or receiving particular nerves as the 

 brain furnishes or receives its own. . . . The continuous thread that is observed 



from the neck to the pelvis is nothing but a series of communications These 



communications are often interrupted, without any inconvenience in the organs to 

 which the great sympathetic goes." That the sympathetic system acts independently 

 of the central nervous system, at least to a great extent, is its most prominent physio- 

 logical characteristic. 



Thus the sympathetic system merits to some extent the terms organic, visceral, 

 or vegetative system, which have been applied to it. Burdach (1819) stated that it 

 might be called the "automatic system," and the term "autonomic system" has more 

 recently been used, but Burdach preferred sympathetic system, which has been inter- 

 nationally adopted by anatomists. 



DEVELOPMENT OF THE CEREBRAL NERVES. 



The nerves which are connected with the brain, supplying the skin and 

 muscles of the head together with certain viscera, are built upon the 

 same plan as the spinal nerves, of which they may be regarded as a continu- 

 ation. They consist of dorsal sensory roots, and ventral motor roots 

 which, however, do not unite to form single nerves. Certain cerebral 

 nerves are wholly sensory and others consist merely of a ventral root, and 



