The Nervous System. 293 



The fibres supplying the visceral muscles with motor 

 power arise from the cervical portion of the cord, and exert 

 their function through the vagus nerve. The viscero-motor 

 nerves are in turn controlled by viscero-inhibitory ; these 

 pass from the inferior roots of the spinal nerves, direct to 

 the tissues through the abdominal spknchnics ; they are, 

 therefore, not connected with the vertebral ganglia. 



It is probable that all the glands of the body are supplied 

 with sympathetic fibres, in the same way as has been 

 demonstrated to occur in the submaxillary gland. 



Sympathetic Ganglia. —We have before noticed that when 

 medullated nerves pass through a sympathetic ganglion, they 

 lose the white substance of Schwann and become non-medul- 

 lated ; they also become more numerous, for nerve fibres 

 originate in the ganglia, arising from the ganglion cells 

 found in this structure. It is not known whether the 

 sympathetic ganglia possess the same properties as the 

 cerebro-spinal ganglia. 



Trophic Influences. — Sympathetic ganglia also exercise 

 through the nerves leaving them, a trophic or nutritive 

 influence over parts. GaskeH's views in connection with 

 this matter are most important. He considers that every 

 tissue has nerves which excite repair, and are termed 

 anabolic, and others which excite waste, and are termed 

 katabolic. We mentioned this theory in connection with 

 the heart, the sympathetic nerves of which excite kata- 

 bolism by increasing the heart's action, whilst the pneumo- 

 gastric exercises processes of repair, its function being to 

 control the heart : it is therefore regarded as an anabolic 

 nerve. 



Sweating is produced through the vaso-motor fibres of 

 the sympathetic, in conjunction with the secretory nerves: 

 section of the cervical sympathetic in the horse leads to 

 sweating on that side of the neck and head (see p. 195). 



For the effect on the secretion of saliva by division of 

 the sympathetic, see p. 106. 



