THE CEREBRUM. 551 



Electric stimulation of the sensor areas is attended by certain motor 

 reactions which vary in accordance with the area stimulated. Thus, when 

 the electrodes are applied to different portions of the occipital lobe the eye- 

 balls are conjugately turned upward, downward, or laterally and to the 

 opposite side; when placed on the upper portion of the superior temporal 

 convolution, the ear is pricked up or retracted, the head is turned to the 

 opposite side and the pupils are dilated; when placed on the hippocampal 

 convolution, there is movement of torsion of the nostril and lips of the same 

 side. 



Ferrier assumed that these movements were the result of the origination 

 of subjective sensations and not an evidence that the area in question is a 

 motor area, in the sense that this term is applied to the areas of the Rolandic 

 region, especially as their destruction is not followed by paralysis of any of 

 the corresponding muscles. This interpretation is supported by the ex- 

 periments of Schafer, which showed that the contraction of the eye-muscles 

 which followed stimulation of the occipital lobe took place between 0.2 and 

 0.3 second later than when the frontal lobe was stimulated; and that as the 

 motor reaction takes place after extirpation of the frontal region, the route of 

 the efferent impulse cannot be to and through the frontal lobe, but probably 

 through some lower center. The same facts hold true for the reactions of 

 the ear-muscles following stimulation of the temporal lobe. 



The view that the cortex of the cerebrum can be divided into separate and 

 independent though physiologically related motor and sensor areas has 

 been questioned in recent years, and a somewhat different interpretation 

 given to the facts. It is believed by many physiologists and neurologists 

 that the so-called motor and sensor areas are so closely related that it is 

 almost impossible to distinguish one from the other either anatomically or 

 physiologically. Thus the Rolandic region is believed to be both motor and 

 sensor in function, the former, however, being more predominant in the per- 

 central, the latter in the post-central, convolution. As these two functions 

 are so intimately blended and their anatomic substrata so difficult of separa- 

 tion, it is thought the term sensori-motor should be employed as more descrip- 

 tive and more in accordance with the facts to the entire Rolandic 

 region. 



This view has been strengthened by the results of the embryologic 

 investigation of Flechsig, which show that different nerve-tracts become 

 medullated or receive their myelin investment at successively later periods and 

 that the tracts which first become myelinated and are hence first functionally 

 active, belong to the afferent system. Among the first to undergo myelini- 

 zation are three tracts numbered by Flechsig i, 2 and 3, which arise largely 

 from the median nucleus of the thalamus and the medial lemniscus and pass 

 to the anterior and posterior convolutions, to the para-central lobule and 

 foot of the superior frontal convolution, and to the foot of the third frontal 

 convolution respectively. It is these fibers which convey nerve impulses to 

 the cortex and furnish information regarding changes taking place in the 

 body itself and thus lead to the performance of muscle movements. This 

 area is therefore primarily a sensor area, an area for body-feelings, cutaneous, 

 tactile, muscle, and visceral, and secondarily a motor area. The afferent 

 fibers to this region become myelinated during the ninth month of intra- 



