THE CRANIAL NERVES 609 



cious, obstinate. He was most inconsiderate of his associates, profane and 

 passionate. From a shrewd business man he was changed to the intellectual 

 level of a child and was regarded by his associates as mentally unbalanced. 



A summary of fifty cases of pathological lesions of the prefrontal areas of 

 the human brain is given by Williamson. The mental traits of thirty-two are 

 summarized in the following terms: "A condition of mental decadence; a 

 dull mental state; loss of power of attention; loss of memory; loss of spon- 

 taneity; the patient takes no heed of his surroundings; sleeping during the 

 greater part of the day, or remaining semi-comatose." Yet these patients 

 are able to walk about and execute well co-ordinated muscular activities of 

 all kinds that do not involve complex intellectual activity. 



The Parietal Association Center. Special mention is made of this 

 association area because there is increasing evidence that it is the parietal 

 region of the brain, rather than the frontal, as popularly believed, that is 

 most intimately concerned with the higher acts and powers of imagination, 

 idealization, and reasoning. It is the region through which the individual 

 maintains his interests and relations with the external world as against his 

 own body. The parietal association center is more closely related to the 

 visual, auditory, and speech centers of the cortex. The great musician 

 Bach had an exceptionally well developed parietal region. 



On the Cortical Centers in General. For purposes of clearness in 

 presentation, the cortical centers have been discussed one by one, but the 

 reader is guarded against the thought that their activities are in any sense 

 isolated. A motor area does not usually act in the absence of sensory or af- 

 ferent stimulation in the actual living body, whether it may do so on occa- 

 sion or not. Neither do sensory impressions arising in the peripheral sense 

 organ make their way over definite tracts to the brain and cortex and arouse 

 sensations alone. Sensations do not occur independent of motor activities 

 on the one hand, and of intellectual acts through the association centers on 

 the other. 



The association centers are the highest co-ordinating regions of the nervous 

 system. They are to the sensory and motor centers what these latter are to 

 the reflex centers of the cord. The difference is one of degree and not of 

 kind. Further, the association centers are probably set into activity by the 

 complex of inflowing or afferent impulses in just the same sense that the 

 spinal reflex centers are set in activity by sensory or afferent stimuli; the 

 condition is, of course, a thousand times more complex. 



THE CRANIAL NERVES. 



The cranial nerves consist of twelve pairs; they appear to arise (super- 

 ficial origin) from the base of the brain in a bilateral series, which extends 

 from the under surface of the anterior part of the cerebrum to the lower end 



39 



