THE CEREBRAL HEMISPHERES 149 



which they may discharge can be inferred with rea- 

 sonable assurance. 



The neurologist's problem is somewhat like that of 

 an electrician who is sent to a large factory building, 

 of which he has no previous knowledge, with orders 

 to prepare a complete wiring chart of the building. 

 Beginning with the generators, he first determines the 

 sources of the current and the various kinds of 

 electric energy there supplied (direct, alternating, 

 high and low voltage, etc.). The feed wires are then 

 followed through their conduits, switchboards, trans- 

 formers, etc., to their respective lamps, heating units, 

 motors, and so on. In the end he has, not only a map 

 of the courses of all of the circuits, but also informa- 

 tion regarding the purpose to be served, the function 

 of each of them. 



So the neurologist builds up his wiring chart of the 

 body and thereby secures tolerably reliable informa- 

 tion about the functions of those deeper parts of the 

 brain whose experimental study is very difficult. The 

 inferences thus drawn have been adequately checked 

 experimentally in a sufficiently large number of cases 

 to demonstrate the validity of the anatomical method 

 when skillfully executed. 



The arrangement of the parts 6f the cerebral hemi- 

 sphere in one of the lowest mammals is illustrated in 

 figures 32 and 23j taken from Obenchain's excellent 

 memoir (1925). In these very lowly South American 

 marsupials the external aspect of the cerebral hemi- 



