THE CEREBRUM 589 



tters, numbers, and perhaps objects. If the visual word area is destroyed 

 ";y disease, word blindness is established, and the patient is unable to under- 

 'and written or printed language because of his inability to revive memory 

 nages of words. Letter and number blindness may or may not be present 

 ccording to the extent of the lesion. 



All the special sense areas may, therefore, be said to consist of two smaller 

 >reas, a sensor and a psychic, e.g., a cutaneous sensor and a cutaneous psychic, 

 visual sensor and a visual psychic, etc.; the former is for the development 

 ,f crude sensation; the latter, more complex in character, is for the correla- 

 x>n and formation of sensations whereby judgments or definite conceptions 

 .re formed (Campbell). 



The Sensori-motor Areas. It will be observed on examination of dia- 

 rams 250 and 251, that each sense area has closely associated with it a 

 ense motor area, each of which is to be regarded, from one point of view at 

 iiast, as a constituent part of the motor area of the cortex. 



On a previous page it was stated that electric stimulation of sensor areas 

 s attended with certain motor reactions in the muscle groups associated with 

 he activities of the sense-organs, reactions which resemble those caused by 

 trong impressions made on the sense-organs by external agents; that some 

 nvestigators, therefore, believed that the areas in question were motor and 

 ,-ensor in function and that their anatomic substrata were so intermingled 

 md so difficult of separation that the term sensori-motor should be employed 

 is more descriptive and more in accordance with the facts; but that the 

 progress of experimental work, together with the accumulation of facts from 

 he clinical and pathologic fields, incline to the view that the groupings of the 

 motor and sensor cells are anatomically and physiologically separate and 

 distinct though related functionally. Corresponding areas are now believed 

 to be present in the human brain. For this reason each of the special sense 

 areas with the exception of the cutaneous, is represented in Fig. 250, as asso- 

 ciated with a motor area, viz.: a gustatory, an olfactory, an auditory and 

 a visual motor area. The cutaneous sensor area is, however, also associated 

 with a cutaneous motor area in the posterior portion of the pre-central con 

 volution These associated motor and sensor areas are here represented 

 not as overlapping, but contiguous, though perhaps interdigitating with 

 each other. Their location and relations are apparent from an examina- 

 tion of the diagrams. From the results of experimental investigations it is 

 .generally believed the sense motor areas are more ^^\^f* 

 sensori-motor reflex actions rather than to voluntary actions and that they 

 constitute the efferent element of a reflex arc, since destruction of the area 

 interferes with the former rather than the latter Hpmnn , trated that 



It will be recalled that the investigations of Flechsig demonstrate 

 from these areas efferent or motor nerves pass through the sense tracts or 

 radTations in the reverse way, to the mid-brain, where they become related 



SZ^crfSS^tS motor cranial nerves which excite to action those 



, n 



