THE KEKVOUS SYSTEM 269 



in shape (see Chap. VII, p. 73), in the number of their 

 dendrites, and in the abundance of their connections with 

 other neurones. The regular arrangement in the cord of 

 central gray matter surrounded by white matter is wanting ; 

 instead, masses of gray matter occur here and there among 

 the bundles of nerve fibers of which the white matter is 

 composed. In the cerebrum and cerebellum the external 

 surface consists of gray matter and is known as the cortex 

 of the cerebrum and cerebellum respectively. These cortical 

 structures form the most complicated system of nervous 

 tissue in the body, and the cerebral cortex is intimately 

 concerned with the highest functions of the brain. (See 

 Figs. 109, 110, and 111.) 



The figures give some idea of the variety and complexity 

 of the neurones of the brain. But however different, at first 

 sight, the brain may be from the spinal cord, the anatomical 

 plan of organization is the same in both; the brain as well 

 as the cord does its work because the connections of its neu- 

 rones with one another bring about coordinated action. The 

 secret of the structure of the brain, as of the cord, lies in 

 the nature of the connections of its units, the neurones, one 

 with another. 



B. THE PHYSIOLOGY OF THE NERVOUS SYSTEM 



Whenever through accident, disease, or otherwise, some 

 portion of the nervous system is destroyed, functions depend- 

 ent upon it are no longer performed, or at least are not per- 

 formed normally. A very large number of observations have 

 been made upon both animals and men in this condition, and 

 these have made it possible for us to obtain some idea of the 

 part played in normal life by each part of the brain and cord. 

 We shall attempt here to sketch only a few of the more im- 

 portant outlines of the picture, which the reader may com- 

 plete by more extensive study of physiology and psychology. 



