THE CORTICAL GRAY MATTER. 183 



mines the intellectuality of the individual (Fig. 54). To acquire 

 knowledge of the external world is thus the function of the posterior 

 association center. Mills calls it the center of "the concrete con- 

 cept" (Fig. 56). It includes three psychic areas, the common 

 sensory, auditory and visual. Flechsig regards the island (of 

 Reil) as the middle association center (Figs. 25 and 56). Lesions 

 in it are associated with paraphasia. 



Destructive lesions of parts of the motor or sensory cortex 

 cause merely loss of certain motions and sensations represented 



Fig- 57- Cortical areas after C. K. Mills. Medial and tentorial surface of 

 cerebral hemisphere. (Brubaker's Physiology.) 



by those parts, but ablation of association centers disconnects 

 the sensory, the psychic and the motor regions and causes aphasia, 

 agraphia, change of temperament, impairment of the so-called 

 moral and intellectual faculties, etc. Ablation of the visual 

 psychic center or auditory psychic center produces mind-blindness 

 in the former and in the latter mind-deafness. 



Cell and Fiber Lamination of the Cerebral Cortex. There 

 is a type of cerebral cortex which, with small but definite varia- 

 tions, prevails throughout the cerebrum, excepting in the visual 



