962 



THE NERVE SYSTEM 



superfrontal; the upper limb seems to be controlled by the midportion of the precentral; while 

 the facial musculature is projected in the ventral part. The motor regions for the tongue, 

 larynx muscles of mastication, and pharynx lie in the frontal opercular part; and the movements 

 of the head and eye are dominated by the medifrontal gyre, adjacent to the precentral. Re- 

 calling the fact that the pyramidal (motor) tract decussates in its course to the primary motor 

 centres it follows that the motor centres in one cerebral hemisphere control the movements of 

 the opposite side of the body. As elsewhere in the cortex, these motor areas gradually pass one 

 into the other and the boundaries are indeterminate. The localization of motor function is 

 rather for coordinated groups of muscles than for individual muscles; as a rule, the most powerful 

 articulation as the thigh and the shoulder, is Realizable frontad in the respective limb centres, 

 while the smaller articulations and those differentiated as regards motihty (digits, etc.) are local- 

 izable more posteriorly. 



2 Sensor Areas. (a) The area for tactile and temperature impressions is more intensely 

 localized in the postcentral gyre and in corresponding order with its neighboring precentral 

 motor areas; that is to say, there is the most intimate intercommunication between the sensor 

 and the motor regions which preside over corresponding parts of the body. So closely coupled 

 are the related sensor and motor cells in the highest category of the reflex arc system represented 

 in the cerebral cortex that both sensor and motor areas are included under the term of somes- 

 thetic or sensomotor area, devoted to the registration of cutaneous impressions, impressions 



FIG. 713. Lateral view of left cerebral hemisphere, showing localization of functions. The schema of the 

 fissures and gyres is the same as in Fig. 635. 



from the muscles, tendons, and joints; in short, the sense of movement. The cortical area 

 embraced by the parietal gyre, together with its extension in the precuneus on the mesal aspect, 

 appears to be devoted to the concrete perception of the form and solidity of objects, and is there- 

 fore termed the stereognostic sense area. 



(b) The auditory area is localized in the middle third of the supertemporal gyre and in the 

 adjacent transtemporal gyres in the sylvian cleft. 



(c) The visual area is most intensely localizable in the region of the calcarine fissure as well 

 as in the cuneus as a whole. There seems to be an interrelation between the visual function and 

 the special type of cortex already described, and chiefly characterized by the stripe of Gennari. 



(d) The olfactory area comprises the uncus, frontal part of hippocampus, indusium, sub- 

 callosal gyre, parolfactory area, and anterior perforated substance. 



(e) The gustatory area has not yet been accurately localized; presumably it lies in the neigh- 

 borhood of the olfactory area in the temporal lobe (uncinate and hippocampal gyre?). 



3. The Language Areas. The cortical zone of language comprises certain specialized areas 

 which take part in the intimate relations of speech to thought expression, to memory, in its 

 reading form to sight, in writing to manual muscular innervation, and in "word understanding" 

 to hearing. 



(a) The emissive (articular} centre for speech is localized in the region of the junction of the 

 subfrontal gyre with the precentral gyre a region known to be intimately related to the control 



