158 THE HUMAN SPECIES 



are arranged in a special order or the cortical structure as- 

 sumes a new form. 



(2) In the structure of the cortex there are several distinct 

 types to be recognised : the motor type, the type of the upper 

 occipital cortex, that of the optic region and that of the 

 olfactory cortex. The distinction between these various 

 structures is shown by the differences in the strata of the 

 large cells (stratum of the large pyramid cells in man), in the 

 presence of the stratum granulosum and in certain peculiarities 

 of the stratum of small cells (small pyramid cells in man) lying 

 immediately under the molecular layer. 



(3) In the cerebrum a transverse fissure was found, a 

 second occurring near the occipital pole, its position bearing 

 a striking resemblance to that of the fissura occipitalis. It 

 marks approximately the boundary between the cortical region 

 named " motor " by the authors, and that situated nearer the 

 occiput, and hence termed by them the upper occipital cortical 

 region. 



(4) A fissura occipitalis in the lower surface of the occipital 

 lobe in the rabbit is probably identical with the fissura calcar- 

 ina. The cortex is here distinguished by the presence of 

 innumerable granule cells, closely crowded together and 

 separated from the molecular stratum only by a thin layer 

 of dark-coloured large cells. In the other lissencephalous 

 animals subjected to examination the stratum granulosum was 

 not so highly developed as in the rabbit, but was nevertheless 

 clearly recognisable. 



(5) The fissura rhinalis marks the commencement of a very 

 striking modification in the cortical structure, indicated by the 

 abundance of dark, large cells in the second stratum, and by 

 the narrowness of the fourth cellular layer. In those cases 

 where a distinct fissura rhinalis is absent the same abrupt change 

 in the cortex nevertheless appears in the corresponding place. 



(6) In the posterior cornu large, dark-coloured ganglion 

 cells are found with large and long-pointed processes, which 

 occur nowhere else in the whole brain. 



(7) The results of the investigations show that the study 

 of the structure of the cerebral cortex, which varies greatly in 

 character, is of the highest importance in studying the con- 



