ANATOMY OF THE NERVOUS SYSTEM 133 



nucleus; (4) the medulla; all the gray matter of the medulla is 

 contained within its nuclei. They constitute the so-called deep- 

 origins of those cranial nerves which arise in the medulla. 



All nerve-ganglia in the Body, using the term ganglia in the 

 restricted sense suggested above, fall into two groups: 1) Those 

 which contain the cell-bodies of sensory neurons; in this group 

 belong all dorsal root-ganglia of spinal nerves (see p. 126), like- 

 wise the ganglia which are found on some of the cranial nerves; 

 (2) the so-called sympathetic ganglia which are described in the 

 next paragraph. 



The Sympathetic System. The ganglia which form the 

 main centers of the sympathetic nervous system lie in two rows 

 (s, Fig. 2, and sy, Fig. 3), one on either side of the bodies of the 

 vertebra. Each ganglion is united by a nerve-trunk with the one 

 in front of it, and so two great chains are formed reaching from 

 the base of the skull to the coccyx. In the trunk region these 

 chains lie in the ventral cavity, their relative position in which is 

 indicated by the dots sy in the diagrammatic transverse section 

 represented on p. 6 in Fig. 3. The ganglia on these chains are 

 forty-nine in number, viz., twenty-four pairs, and a single one in 

 front of the coccyx in which both chains terminate. They are 

 named from the regions of the vertebral column near which they 

 lie; there being three cervical, twelve thoracic, four lumbar, and 

 five sacral pairs. 



Each sympathetic ganglion is united by communicating branches 

 with the neighboring spinal nerves, and near the skull with various 

 cranial nerves also; while from the ganglia and their uniting cords 

 arise numerous trunks, many of which, in the thoracic and abdom- 

 inal cavities, form plexuses, from which in turn nerves are given 

 off to the viscera. These plexuses frequently possess numerous 

 ganglia of their own; two of the most important are the cardiac 

 plexus which lies on the dorsal side of the heart, and the soZar 

 plexus which lies in the abdominal cavity and supplies nerves 

 to the stomach, liver, kidneys, and intestines. Many of the 

 sympathetic nerves finally end in the walls of the blood-vessels 

 of various organs. To the naked eye they are commonly grayer 

 in color than the cerebro-spinal nerves. 



