SYMPATHETIC SYSTEM. 103 



Describe the abdominal sympathetic. 



In the abdomen the sympathetic consists mainly of an aggrega- 

 tion of ganglionic enlargements situated upon the coeliac artery, 

 known as the semilunar or coeliac ganglion. It communicates with 

 the thoracic ganglia and with all the lumbar nerves. From this 

 centre proceed a multitude of diverging and inosculating fibres, 

 which, from their common origin and radiating course, are called 

 the solar plexus. Its secondary plexuses, accompanying the branches 

 of the abdominal aorta, are distributed to the stomach, intestines, 

 spleen, pancreas, liver, kidney, and internal organs of generation. 



How are the pelvic plexuses derived? 



From four or five pairs of ganglia situated on the anterior por- 

 tion of the sacrum and terminating in the ganglion impar, lying 

 upon the coccyx. Its fibres join those from the solar plexus, and 

 are distributed with them along the course of the branches of the 

 internal iliac arteries. 



Describe the sensibility and motor influence of the sympathetic 



nerves. 



It will be remembered that the spinal nerves, both afferent and 

 efferent, act very quickly upon the tissues supplied by them ; the 

 sympathetic nerves act more slowly. Thus, if the afferent nerve 

 or a ganglion or its efferent nerve be stimulated, there is a slow 

 wave-like series of motions set up in the parts supplied, which con- 

 tinue for some time after the stimulus is withdrawn. This is par- 

 ticularly well seen in the intestinal peristalsis which may be excited 

 by stimulation of the intestine or of the semilunar ganglion or of 

 the branches of the solar plexus. 



What is the effect of the sympathetic nerves upon special senses ? 

 The dilatation of the pupil is effected through it, and probably 

 the accommodation is acted upon by fibres other than the oculo- 

 motorius, which come through the lenticular ganglion. The tensor 

 tympani muscle is supplied from the otic ganglion. 



What is the vaso-motor function of the sympathetic ? 



The muscular coats of the blood-vessels, especially of the arteries, 

 are under the control of the sympathetic filaments and plexuses, 

 which accompany them throughout their entire system. These 

 fibres are of two kinds as regards their function : (1) vaso-con- 

 strictor and (2) vaso-dilator fibres. 



