626 E. H. J, SCHTTSTEi;. 



is bounded behind by the precentral area, below by the 

 calloso-marginal fissure, and extends forward for a consider- 

 able distance. Its anterior boundnry crosses the supero- 

 mesial border about 2 cm. in front of the precentral area in 

 the chimpanzee, and somewhat further forwai'd in the orang-. 

 On the lateral surface it forms a zone lyini^- in front (if the 

 precentral area, which is brond above, but becomes narrower 

 lower down, being bounded in front for a short distance by 

 the sulcus arcuatus. 



As it nears the Sylvian fissure it extends forwards over the 

 lower portion of the sulcus arcuatus and occupies a more or 

 less rectangular area bounded above by the sulcus rectus and 

 below by the superior limiting sulcus of the island of Reil — 

 the part of the hemisphere which, according to Campbell, 

 corresponds to the pars basilai'is of the human brain. In 

 front it invests the upper end of the sulcus fronto-orbitalis, 

 ''then turning abruptly downwards, and still following the 

 fronto-orbital sulcus, it coats the convolution forming its 

 anterior wall and is finally arrested well down on the inferior 

 (orbital) surface by the sulcus orbitalis." 



In Brodmann's description of the brain of Cercopithecus 

 the area which corresponds to Campbell's intermediate pre- 

 central is occupied by three types of cortex. Type 6, which 

 agrees in structure with the interraedinte precentral, has 

 approximately the same extent on the mesial surface and on 

 the upper and middle portions of the lateral surface, but it 

 never extends far beyond the sulcus arcuatus, which lies along 

 its whole length just behind the anterior boundary. The 

 region roughly corresponding to the pars basilaris is occupied 

 by type 10, which in the orbital surface gives place to 

 type 11. 



Type 11 resembles type G in the absence of a layer of 

 granules but differs from it in the following points ; (1) The 

 external and internal layers of large pyrami(]s (Brodmann's 

 layers iii h and v) are fused to form a clearly delimited band, 

 the cortex is narrower, and to judge from the photographs 

 the cells are considerablv smaller. 



