CORTICAL CELL LAMIXATIOX OF PAPIO HAMADUYAS. 623 



narrow strip, sucli as is figured, hardly shows any lamination, 

 but if a wide area of cortex is examined under the low power 

 of the microscope one can distin<^uisli (1) an upper zone 

 (iii a) consisting mostly of medium-sized pyramids, which 

 stretches downwards to a depth of about "8 mm, (2) A 

 tendency to form a definite layer of large pyramids (iii h) at 

 a depth of ■9-1*2 mm. from the surface. The size of these 

 cells may be 30-50 /z in length by 20-25 ju in breadth. (3) A 

 stratum, rather poor in cells, extending from r2-l'4 mm. 

 (4) Another, but less well-defiued, layer of large pyramidal 

 cells (v) at 1'4-1'6 mm. These cells are in some places rather 

 larger than those at iii 6, in other places about the same size 

 or rather smaller ; they are in all places much less numerous. 

 A few granule cells and small triaugular and irregular-shaped 

 cells are present between, and interspersed with, both the 

 upper and lower layers of large pyramids. 



(vi) Lamina multiformis occupies the rest of the cortex ; it 

 contains cells of varied shapes, the most prevalent being 

 roughly triangular cells with long processes extending both 

 upwards and downwards. 



Extent and Boundaries. — Tiie precentral cortex on the 

 mesial surface is bounded below by the sulcus cinguli ; on the 

 lateral surface it extends posteriorly to the bottom of the sulcus 

 centralis; below it falls considerably short of the Sylvian fissure. 

 Along its free anterior and lower border it passes gradually 

 into the anterior precentral type. 



The anterior precentral type is also bounded below on the 

 mesial surface by the sulcus ciuguli; along the supero-mesial 

 border it extends to more than half the distance between the 

 upper end of the sulcus centralis and the frontal pole. Its 

 upper anterior extension forms a broad band on the lateral 

 surface, the posterior part of which is bounded below by the 

 horizontal limb of the sulcus arcuatus. The vertical portion of 

 that fissure serves as the anterior boundary of the narrow strip 

 of this cortex, which lies in front of the lower portion of the 

 precentral area. Approaching the Sylvian fissure the anterior 

 precentral type alters considerably in character; the large 



