THE CEREBRUM 601 



as their destruction is not followed by paralysis of any of the corresponding 

 muscles. The view that these reactions are reflex in character has been 

 substantiated by the anatomic fact that in the immediate neighborhood of 

 each sense area, though not overlapping it, motor cells are present from 

 which efferent nerve-fibers pass in close relation to the afferent fibers, toward 

 and to lower nerve-centers and presumably to the centers of origin of related 

 cranial nerves. This interpretation is supported by the experiments of Schaf er, 

 which showed that the contraction of the eye muscles which followed stimula- 

 tion 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 can- 

 not 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 follow- 

 ing stimulation of the temporal lobe. 



For these reasons it came to be believed that each sense area is associated 

 with a motor area, though the two are not identical but separate in their 

 distribution. The associated motor areas assist in the formation of a 

 mechanism by which reflex movements are executed when sense organs 

 are stimulated. 



This being the case with animals the presumption is that the same 

 facts hold true for human beings. The progress of experimental work, 

 together with the facts obtained from clinical and pathologic fields support 

 the views that the sensor areas of the human brain are associated anatom- 

 ically with separate and distinct though with physiologically related 

 motor areas. For this reason each of the special sense areas, with the 

 exception of the cutaneous, is represented in Figs. 247 and 248, as associ- 

 ated 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 that the sense motor areas are more particularly related to 

 sensori-motor reflex actions rather than to volitional 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. 



It will be recalled that the investigations of Flechsig demonstrated that 

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

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

 to the nuclei of origin of the motor cranial nerves which excite to action those 

 muscles associated with the sense organs in their adjustments to the stimulus. 

 Thus electric stimulation of the gustatory motor area gives rise to movements 

 of the lips and tongue; of the olfactory motor area, to movements of the nos- 

 trils, etc., as in sniffing; of the auditory motor area to movements of the head 

 and eyes to the opposite side and to pricking of the ears; of the visual motor 

 area to movements of the eyeballs and head in different directions, in accord- 

 ance with the part stimulated. All these movements are similar to those 

 which follow gustatory, olfactory, auditory, and visual sensations, evoked 

 by unexpected stimulation of the peripheral sense-organs themselves. 



