

THE CENTRAL NERVOUS SYSTEM. IOI 



ganglion corresponding with each spinal nerve root, but the upper four 

 thoracic ganglia are fused into one larger mass, the stellate ganglion. In 

 the cervical region there are in most animals only two ganglia, inferior 

 and superior, united by the cervical sympathetic nerve. The pre-gang- 

 lionic sympathetic fibres leave the anterior root in the thoracic and upper 

 lumbar region as a series of small nerves, the white rami communicantes, 

 each of which enters the corresponding ganglion of the lateral sym- 

 pathetic chain. Some of these fibres, including those which carry 

 impulses to the blood-vessels of the skeletal muscles and skin, and to 

 the hairs and sweat glands, have their cell stations in one or other of 

 the sympathetic ganglia ; and the post-ganglionic fibres form small 

 nerves (called grey rami), one of which joins each of the spinal nerves. 

 The sympathetic fibres which supply the blood-vessels and other 

 structures of the head leave the spinal cord by the first to the fourth 

 or fifth thoracic white rami, and pass through the stellate ganglion up 

 the cervical sympathetic nerve to the superior cervical ganglion ; their 

 cell stations lie in this ganglion, and the post-ganglionic fibres leaving 

 it are distributed to the blood-vessels, salivary glands, and other 

 structures in the head. 



The fibres which supply the heart leave the spinal cord by the second 

 and third thoracic white rami, and have their cell station in the stellate 

 ganglion, from which post-ganglionic fibres pass directly to the heart. 



The fibres which are distributed to the abdominal viscera issue from 

 the spinal cord by the lower six thoracic and the first lumbar white rami, 

 pass through the corresponding ganglia of the sympathetic chain without 

 forming a cell station, and are gathered up into two large nerves, one on 

 each side, known as the splanchnic nerves. These enter two large ganglia, 

 the semilunar ganglia or solar plexus, in which lie the cell stations of almost 

 all the fibres running in the splanchnic nerves. Some of the post-gang- 

 lionic fibres leaving these ganglia are distributed to the blood-vessels of 

 the abdominal viscera, while others supply the walls of the digestive tract. 

 Fibres also pass along the white rami of the upper lumbar nerves to 

 the inferior mesenteric ganglia, from which post-ganglionic fibres run 

 .in the hypogastric nerves to be distributed to the pelvic organs. 



Nicotine, in small doses, first stimulates and then paralyses the 

 synapses between the pre-ganglionic fibres and the nerve cells in the 

 autonomic ganglia, thereby preventing the passage of an impulse 

 through the cell stations ; it does not affect the nerve fibres themselves. 

 By means of nicotine, the course taken by the autonomic fibres and the 

 situation of their cell stations have been determined. The drug is 

 painted on a ganglion, and the fibres passing to and from it are 

 stimulated; if stimulation of the fibres passing to the ganglion is 



