THE NERVOUS SYSTEM. 87 



teal descends along the outer side of the popliteal space 

 and divides an inch below the head of the fibula into 

 the anterior tibial, which supplies the flexors and skin 

 of the ankle-joint, and the musculo-cutaneous, which 

 sends branches to the skin of the lower leg and the dor- 

 sum of the foot. 



The Sympathetic System. Joined to the cerebro-spinal 

 system by intervening cords is the sympathetic system. 

 This is made up of two series of ganglia, one on either 

 side of the spinal column, connected by longitudinal 

 bands and extending from the base of the skull to the 

 coccyx. They do not form an independent nervous 

 system, each ganglion, which seems to resemble the 

 motor cells of the spinal cord, being connected by motor 

 and sensory fibers with the cerebral system. 



The sympathetic nerves are mostly gray, non-medul- 

 lated fibers and are distributed to viscera, secreting 

 glands, and blood-vessels, whose movements are in- 

 voluntary and feelings obtuse. They form networks 

 upon the heart and other viscera and send branehes to 

 the cranium to the organs of special sense. There are 

 three main plexuses: The solar plexus behind the stom- 

 ach, which supplies the abdominal viscera; the hypo- 

 gastric plexus in front of the prominence of the sacrum, 

 whose nerves go to the pelvic organs; and the cardiac 

 plexus behind the aortic arch for the thoracic viscera. 



Over these nerves one has no control. A blow in the 

 region between the costal cartilages and below the ster- 

 num is a solar plexus blow and is very upsetting. 



The sympathetic system serves to maintain vitality 

 in all the important portions of the system and one of 

 its important functions is to keep up communication 

 between one part and another, so that when any organ 

 is affected the others will act accordingly and help out 

 to the best of their ability. 



