THEM'S YMPATHETIC NERVE SYSTEM. 565 



the cells of the sympathetic ganglia, vertebral, pre- vertebral, and 

 peripheral, are distributed ultimately and directly to but two struc- 

 tures: viz., non-striated muscle and secretory epithelium. Moreover, 

 there is no evidence to warrant' the assumption that the^ ^plffiires 

 (wifh the exception of the heart) ever receive nerve impulses directly 

 from the spinal or cranial nerves. All nerve impulses which influence 

 their '"activities," 1 eftner in the way of excitation or inhibition, emanate 

 directly though not originally from the sympathetic ganglion cells. 

 Since non-striated muscles are found in the walls of blood-vessels, 

 in the walls of hollow viscera, and around hair-follicles, and since 

 secretory epithelium is found in all glands, there is every reason to 

 believe that the ganglia in some way are associated with vasp-motor 

 and vaso-inhibitor, viscero-motor and viscero-inhibitor, pilo-motor 

 and secretor phenomena. 



The Anatomic Relations of the Sympathetic and Cerebro- 

 spinal Systems. The sympathetic ganglia are connected with the 

 spinal nerves by two branches, one white, the other gray in color, 

 and known respectively as the white and gray rami communicantes. 

 These two rami differ somewhat in their topographic distribution. 

 The white rami are found passing only from those spinal nerves 

 included between the first thoracic and second or third lumbar and 

 their corresponding ganglia. The gray rami, on the contrary, are 

 foimct passing from the ganglia to eacli of the spinal nerves. In the 

 cervical region, where the ganglia do not correspond in number with 

 the cervical nerves, each ganglion gives off two or more gray rami. 

 In man the superior cervical ganglion sends gray rami to the first 

 four cervical nerves; the middle and inferior ganglia apparently 

 send gray rami to the fifth and sixth, the seventh and eighth nerves 

 respectively. 



The white rami are composed of fine medullated nerve-fibers 

 which arise from nerve- cells situated in the lateral portion of the 

 gray matter in the thoracic and lumbar regions of the spinal cord. 

 From this origin they pass forward into the ventral roots of the 

 spinal nerves, in which they are contained until the spinal nerve 

 formed by the union of the ventral and dorsal roots divides into its 

 anterior and posterior divisions. At this point the fine medullated 

 nerve-fibers leave the common trunk and pass forward into the cor- 

 responding vertebral ganglion, around the cell-bodies of which some 

 of the fibers t once arborize. Other fibers, however, pass through 

 this ganglion and ascend or descend the cord for a variable distance, 

 and arborize around the cells of more or less distant ganglia ; others 

 again pass forward into the pre-vertebral and even the peripheral 

 ganglia before they finally terminate. The nerve-cells in the spinal 

 cord are thus brought into relation with the ganglia of all three 

 chains, though for each cell there is but one ganglion terminal, 



