110 PHYSIOLOGY AND TEMPERANCE, 



most outlying parts. The force generated by the brain cells 

 and thus employed is like electricity; but it is something 

 more, which no physiologist has yet been able to define. 



5. The Cerebrum. The upper and front part of the 

 skull contains the cerebrum. It forms about seven-eighths 

 of the total weight of the brain. It is divided by a deep 

 fissure into two halves, the right and left hemispheres. 

 Each half is in itself a brain, the one half supplementing 

 the other, as one hand or one eye does the other. Injury 

 to the brain, with loss of brain substance on one side, does 

 not necessarily cause loss of brain power. 



6. The Cerebellum. Immediately under the back part 

 of the cerebrum, but separated from it by a firm membrane, 

 lies the cerebellum, or lesser brain. It is about the size of 

 the fist. The convolutions are not so irfegular as in the 

 cerebrum. The gray matter dips down into the white sub- 

 stance in parallel ridges, and is so arranged as to give its 

 internal appearance a resemblance to a tree with branches 

 and leaves. This is called the arbor vitce, or tree of life. 

 The cerebellum is the nerve centre for controlling the volun- 

 tary muscles. It is also made up of two halves. 



7. The Medulla Oblongata. The medulla oblongata is 

 the upper thickened end of the spinal cord, and forms the 

 connecting link between it and the brain. It is about an 

 inch and a quarter in length, and is thicker in its upper than 

 its lower part. It also is divided into two symmetrical halves. 

 The medulla oblongata consists of white and gray matter. 

 The gray matter, which in the brain is on the surface, and 

 in the spinal cord is in the interior, is continued up from the 

 latter in the interior until it reaches the upper part of the 

 medulla, when it begins to show on the surface. 



The medulla oblongata is a very important centre, for from 

 it pass off the nervps which control breathing, swallowing 

 and the action of the heart. Injury here is very sudden and 

 serious in its effects. 



