410 BIOLOGY FOR BEGINNERS 



gether in perfect harmony, we realize how important is this co- 

 ordination of muscular action by the cerebellum. Without it, 

 though the cerebrum might originate the impulse to do a certain 

 act, no regulated useful motion could result. 



Medulla. The spinal bulb (medulla) is really an enlargement of 

 the spinal cord but is within the skull and closely attached to the 

 cerebellum. It is about the size of a walnut and is located at the 

 extreme base of the brain. 



The spinal bulb is the center of control of respiration, circula- 

 tion, secretion, movements of digestive organs and of swallowing, 

 as well as other similar automatic and unconscious activities. 

 Naturally, death follows injury to this vitally important part of 

 the brain, though severe damage to the other parts may not be 

 fatal. 



Spinal Cord. The spinal cord extends from the medulla through 

 the protective bony arch of each vertebra, down almost the whole 

 length of the spine, and from it branch the nerves that supply all 

 parts of the body, except those which spring from the brain directly. 

 The spinal cord is not merely a large nerve trunk, however, but is 

 the center of many involuntary muscular actions (reflex actions) 

 of the body and limbs. If we touch a hot stove, we do not have to 

 think to remove our hands. If something comes near an eye, we 

 do not have to depend on the brain to close the eye. Voluntary 

 action would take too long and injury would result before the brain 

 could have time to act, so all such reflex actions are centered in the 

 spinal cord and operate automatically but not unconsciously as do 

 the motions of the internal organs controlled by the medulla. 



The spinal cord, then, has two functions: 



(1) A connecting trunk between brain and other nerves. 



(2) The center of reflex action. 



Sympathetic System. On each side of the spinal column but 

 inside the body cavity are two rows of nerve ganglia which are 

 connected with each other and with the brain and spinal 

 cord. 



From this double nerve chain extend branches to most of the 

 internal organs and to other ganglia located in the chest and ab- 



