rORTICAL CKLL LAMIXATION OF PAl'IO HAMADKYAS. 621 



anterioi" end is bifurcated in the right lieinisphere. One or 

 two shallow grooves lie between this and the sulcus occipi- 

 talis inferior. 



The sulcus calcarinus [cal.) at its anterior end joins 

 the fissura hippocampi ; it runs a sigmoid course backwards, 

 to end in a long bifurcation near the occipital pole. The 

 upper branch is by far the longest, and its upper end just 

 reaches the lateral surface of the hemisphere. In the right 

 hemisphere it gives off a short downward branch. 



Frontal Lobe. 

 Precentral (Motor) Type (fig. 1^ 



This type of cortex is characterised by its great depth, 

 which reaches to over 2"7 niiu., the presence of the Betz cells, 

 and the absence of a distinct layer of ''granules.'^ Tlie 

 drawing (fig. 1) is taken from the lateral surface of the 

 hemisphere a short way in front of the upper end of the 

 sulcus centralis. Here the breadth of the cortex is about 

 2*7 mm., but only the upper 2'4 mm. are drawn. The Betz 

 cells occupy a broad zone, otherwise i-ather poor in cells, 

 which stretches from 1"3-1"9 mm. from the surface. They 

 appear to be larger here than in other parts of the pre- 

 central area. The cell bodies of the largest are about 70 /x 

 in length by 50 fx in breadth, but the massive processes given 

 off from the apex and base render accurate measurements 

 impossible, since it is difficult to say where the cell-body 

 ends and the bases of the apical process or other dendrites 

 begin. These cells are slightly smaller on the mesial surface, 

 and gradually diminish in size as one passes downwards over 

 the lateral surface towards the Sylvian fissure. About half- 

 way down they measure only 50 x 30 /i. 



The other cell lavers are as follows : 



