CENTRAL NERVOUS SYSTEM. 253 



fibres bringing in impulses which arise through the stimulation of the skin and 

 muscles. It has been suggested, to be sure, that separate localities form the 

 seat for the dermal and muscular sensations. Ferrier indicated the limbic 

 lobe, especially the hippocampal gyrus, while Horsley and Schafer argued 

 for the gyrus fornicatus. At present, the weight of evidence is in favor of 

 the location of the centres for dermal and muscular sensations in the central 

 gyri, a part just caudad to and a part overlapping the area stimulation of 

 which causes the muscles of the trunk and limbs to contract. Both in 

 monkeys and in man defects in sensation are not permanent after limited 

 lesions of the cortex, but, as suggested by Mott, the wide distribution of the 

 incoming impulses would explain this result. 



Thus the entire portion of the cortex to which a definite function can be 

 assigned must be looked upon as containing fibres which bring impulses into 

 it, and cell-bodies which by their discharge send impulses to other divisions 

 of the central system as well as to other parts of the cortex itself. All parts 

 of the cortex having assigned functions give rise on stimulation to move- 

 ments ; but in the case of the sensory areas, so called, they involve the con- 

 tractions of only those muscles controlling the external sense organ, as the 

 eyeball, external ear, tongue, and nostrils. 1 Though physiologically impor- 

 tant, and in the case of the eye reaching a high degree of refinement, they 

 are quantitatively very insignificant when compared with the responses to be 

 obtained from stimulating the "motor region," from which contractions of 

 the larger skeletal muscles are obtained. Hence the usual terms " sensory " 

 and " motor " do not completely characterize the corresponding regions, 

 though they emphasize their most striking features. 



Determination of the Sensory Areas. — Using as a guide the appearance 

 of the medullary sheaths upon the projection-fibres of the cerebral cortex of 

 man during the last months of foetal life and shortly alter birth, Flechsig 2 

 lias been able to outline the sensory areas in the cortex with great clearness. 



The illustrations from Flechsig (Figs. 109, 110) show the parts of the 

 brain where the projection-fibres can be determined at a time when these 

 fibres constitute all or almost all the medullated fibres connecting the cortex 

 with the stem and basal ganglia. By thus marking out in color on the 

 developing cortex the portions concerned, there are seen to be four main 

 areas: First, the area connected with the olfactory trad (olfactory area), 

 involving the uncinate gyrus, the gyrus hippocampi, and the part of the gyrus 

 fornicatus nearest the callosum. Second, the area connected with the optic 

 radiation (visual area), where tin; fibres in question are mosi abundant about 

 the calcarine fissure. They appear, however, all through the cuneus and 

 extend to the cortex which surrounds it on the ventral and lateral aspects of 

 the occipital lobe. Third, we have (auditory area) the portion of the cortex 

 which covers the transverse gyri in the Sylvian fissure and the first temporal 

 gyrus where the former join it. This area is occupied by the project ion- 



1 Ferrier : Functions of the Brain, 1876. 

 'Flechsig: Gehim und Seele, Leipzig, 1896, 



