522 



PHYSIOLOGY 



: stellate ' ganglion. At the bottom of the chain there is only one 

 coccygeal ganglion for the coccygeal vertebrae. 



In the abdomen is a second system of ganglia, in special connection 

 with the abdominal viscera, lying in front of the aorta and surrounding 

 the origins of the large arteries to the alimentary canal. These are 

 the semilunar or solar ganglia, the superior mesenteric and the inferior 

 mesenteric ganglia. 



In the organs themselves we find a third system of ganglion- cells, 

 either scattered or collected to form small ganglia. These isolated 

 ganglion cells as a rule have no connection with the fibres of the 



FTG. 236. Diagram of spinal segment with its nerve- 

 roots, somatic and visceral. (G. D. THAKE.) 

 (The visceral roots are represented in red.) 



sympathetic system, but, as we shall see later, lie on the course of 

 the impulses descending by other nerves of the autonomic system, 

 e.g. the vagus or the pelvic visceral nerves. The three systems of 

 ganglia have been distinguished as the lateral, collateral, and terminal 

 ganglia. 



The ganglia of the sympathetic chain are connected with all the 

 spinal nerves, just after they have given off their posterior divisions. 

 by means of the rami communicantes. These rami communicantes 

 are of two kinds : white rami consisting of small medullated fibres, 

 and grey rami composed almost exclusively of non-medullated nerves. 

 It has been shown by Gaskell that the white rami are formed by 

 fibres which have their origin in the spinal cord and perhaps in the 

 posterior root ganglia ; whereas the grey rami represent fibres which, 

 arising in the sympathetic ganglia, run back to join the spinal nerves. 

 The visceral outflow represented by the white rami is limited to a 

 distinct region of the cord, viz. from the first thoracic to the third 

 or fourth lumbar nerve- roots ; whereas the grey rami pass from the 

 sympathetic to all the spinal nerve-roots. It is found by experiment 

 that stimulation of a limited number of white rami produces all the 



