Chap. XIX] THE NERVOUS SYSTEM 383 



supplies the extremities and parts of the body in front of the spine. 

 The posterior division suppHes the muscles and skin of the back of 

 the head, neck, and trunk. Each anterior division connects with 

 the sympathetic system by means of fibres which pass from the 

 nerve to the sympathetic system and vice versa. Previous to 

 their final distribution in the cervical, sacral, and lumbar re- 

 gions these nerves form plexuses known as the cervical, sacral, 

 and lumbar plexuses. In passing to the viscera, muscles, skin, 

 etc., these terminal nerves follow the same pathway as the blood- 

 vessels. 



Names of peripheral nerves. — Many of the larger branches 

 given off from the spinal ner^'es bear the same name as the artery 

 which they accompany, or of the part which they supply. Thus 

 the radial nerve passes down the radial side of the forearm, in com- 

 pany with the radial artery ; the intercostal nerves pass between 

 the ribs in company with the intercostal arteries. 



Functions of the spinal cord : — 



(a) Conduction, -or the conveyance of impulses and sensations 

 between the centres and the periphery. 



(b) Reflex action, i.e. the origination of an impulse or action 

 in response to a stimulation from the periphery, without of 

 necessity involving the brain in the act or even without con- 

 sciousness of the reflex act on the part of the individual. 



(c) Automatic acts, i.e. acts set up primarily in the cells of 

 the cord by the cells themselves, and not as a result of stimula- 

 tion by brain cells (voluntary acts) nor as result of peripheral 

 stimulation. 



(d) Inhibition of reflex acts. — If every outside stimulation 

 were allowed its full effects in the setting up of reflex acts, the 

 body would be on " the jump " all the time. This overactivity 

 is checked unconsciously by the cells of the spinal cord endowed 

 with this function. 



(e) Transference, i.e. an apparent transferring of impulses 

 from one set of fibres to another. 



BRAIN 



The brain, the most complex and largest mass of nervous 

 tissue in the body, is contained in the complete bony cavity 

 formed by the bones of the cranium. It is covered by three 



