THE BRAIN 



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the vagus, the tenth in the series. In all there are twelve 

 pairs of cranial nerves. They are of very unequal size 

 and do not show the regular separation into roots that 

 has been described for the spinal system. In the cranial 

 nerves there is an overwhelming preponderance of 

 afferent fibers. This is associated with the existence of 

 the important sense-organs of the head, the eye, the ear, 

 and the nose. 



The Human Brain. By far the largest part of the 

 cranial cavity is occupied, in man, by the great mass 

 of nervous tissue which we call the cerebrum. This 



FIG. 25. The human brain from the left. The main mass is the 

 left cerebral hemisphere. The cerebellum, with its narrow convolu- 

 tions, is below and behind. The medulla bears the stumps of several 

 cranial nerves. 



is the " highest" division of the brain in an anatomic 

 and in a physiologic sense. At the first glance one is 

 impressed by its curiously convoluted surface. It is 

 deeply scored by winding furrows. A profound cleft, 

 running longitudinally in the mid-plane, divides it 



