132 HUMAN PHYSIOLOGY 



by relays through the remaining portion of the brain- 

 stem, reaching the cortex at last in what is called 

 the temporal lobe. The majority of impulses from the 

 right ear are said to be brought to the cortex on 

 the opposite side although a fraction seem to reach the 

 station on the side of their origin. Impulses from the 

 nose, adapted to cause sensations of smell, are distributed 

 near their point of entrance into the cerebrum on its 

 under surface. There is some uncertainty as to the 

 cerebral localization of taste. Behind the motor areas 

 in the ape, and probably in man, there are strips of the 

 cortex within which many sensory impulses from the 

 body in general seem to be focused. 



Association Areas. As we have pictured the cere- 

 brum it has, on each side, several areas of a receptive 

 function and one well-marked area from which impulses 

 take their departure to initiate movements. If an 

 animal is to behave in a normal manner, that is, to be 

 guided by its circumstances in what it does, there must 

 be connecting links between the receptive and the dis- 

 charging stations. The higher the organization the 

 more devious and difficult to trace are these connecting 

 links. There may be short cuts between sensory and 

 motor regions insuring certain reactions of a reflex type 

 but many of the ways of communication are most in- 

 direct. It is supposed that they are made by inter- 

 mediate portions of the cortex to which we give the 

 name of the association areas. These are not united 

 by fibers with the brain-stem but only with each other 

 and with the sensory and motor fields. Fibers which 

 run between the cortex and the brain-stem or cord are 

 called projection fibers; they connect higher with lower, 

 or lower with higher, levels. Fibers which run from 

 point to point in the cortex are called association fibers. 

 According to these definitions the association areas have 

 no projection fibers. 



It is natural to consider the association centers as 

 the highest of all in the character of their service. They 



