THE CENTRAL NERVOUS SYSTEM. 



103 



inferior mesenteric ganglia. The nerves convey constrictor impulses 

 to the blood-vessels of the pelvic organs and inhibitory impulses 

 to the muscular coats of the colon, uterus, and bladder. 



(5) Fibres are also contained in all the white rami which have 

 their cell station in the lateral chain of ganglia, the post-ganglionic 

 fibres passing usually, but not always, into the corresponding spinal 

 nerve to be distributed to the blood-vessels of the muscles and skin, 

 and to the sweat glands and hairs in the area supplied by that nerve. 



It will be noticed that many organs are supplied by two sets of 

 fibres having opposite functions. 



FUNCTIONS OF THE GANGLIA. 



The cells of the ganglia serve as distributing centres, and each 

 pre-ganglionic fibre arborises round a number of cells, so that the post- 



Sp.cord 



Post-gangliomc fibre- 



' Pre-ganglionic fibre 

 -Hypogastric nerves 



FIG. 32. Diagram showing the structures concerned in the "axon-reflex" 

 referred to in the text. (Starling's Principles of Physiology.} 



ganglionic fibres are much more numerous than the pre-ganglionic 

 fibres. 



At one time various reflex actions were attributed to the sympa- 

 thetic ganglia, but these have been proved to be not true reflexes, but 

 pseudo- or axon-reflexes. For example, when the nerves connected 

 with the inferior mesenteric ganglion are divided, with the exception of 

 the right hypogastric nerve to the bladder, stimulation of the central 

 end of the left hypogastric nerve causes contraction of the right half of 

 the bladder. This is due to the fact that some of the fibres leaving the 



