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lobe. This posterior part, with the exception of its first convohitions, 

 is divided into one median and two lateral portions by tlie sulci 

 paramediani, which run parallel to the median line. 



Consequently all that is lying between the two paramedian sulci 

 forms the median part of the lobus posterior, all that is lying 

 to the right and to the left of tiieni forms the lateral part of 

 this lobe. 



In figure II sub 11 we find the sulcus intercruralis. This furrow 

 is lying in the middle of the lobus ansiformis, (fig. I). The convo- 

 lutions that start originally from the median line as crus primum 

 (fig. II sub 9) and bend gradually, when arrived in the ultimate 

 lateral part, to return thence as cms secundum (fig. II sub 10) to 

 the median part, take before reaching it another bent, this time 

 straight backward ; to continue further as lobus paramedianus (fig. 

 II sub 12) parallel to the sulcus paramedianus. 



In describing further the lobus posterior we will confine ourselves, 

 for the sake of convenience, to the left half. 



Of course in fig. I and II all that is lying to the left of the 

 sulcus paramedianus belongs to the lateral part, and consequently 

 may not be reckoned to the lobus simplex, the convolutions of this 

 latter, according to Bolk, continuing Avithout any interruption from 

 the right to the left. 



Applying this test to fig. I, we find that the extreme end of the 

 left sulcus paramedianus is stopped by a convolution indicated sub 

 5 fig. II. 



Thence it might be concluded, that the convolutions indicated 

 sub 5 and 6 in fig. II, accordingly lying above the sulci paramediani 

 and below the lobus anterior, form the lobus simplex. 



On a closer examination of the lowest of these two gyri, i. e. 

 the gyrus sub 5, we find however, that to the left of the white 

 spot (the end of the dotted line), in the lateral part of the gyrus 

 therefore, a narrow furrow may still be observed, that does not 

 continue to the median line. According to Bolk therefore, this con- 

 volution does not belong to the lobus simplex, as the incomplete 

 furrows in this lobe, like those in the lobus anterior, ought to start 

 from the median line. 



The cause, why the interruption of this gyrus sub 5 is not, as 

 usually, visible on the surface, must be sought in the fact that the 

 sulcus paramedianus disappears in the depth, and does not therefore 

 penetrate into this convolution on the surface. 



The last convolution, sub 6, fulfills in every respect the conditions 

 claimed by Bolk for the convolutions of the lobus simplex ; as it 



