624 E. H. J. SCHUSTER. 



pyramids, both supra- aud sub-gi-anular, become smaller and 

 more densely packed together, and the lamina granularis 

 interna is more easily recognisable. In this condition the 

 cortex is prolonged forward beyond the lower end of the 

 sulcus ai'cuatus, where it passes gi-adually, on the one hand, 

 into the frontal, and, on the other, into the posterior orbital 

 type. In structure tiiis lower forward extension of the 

 anterior precentral bears a marked resemblance to the 

 anterior part of the posterior orbital cortex. In position it 

 has some points in common with Brodmaun's type 10, which 

 it resembles in having a layer of granules distinguishable but 

 not well developed. 



Posterior orbital type (fig. 5) 



The position of the particular strip of cortex shown in 

 fig. 5 was near to the posterior border of the orbital surface 

 just lateral to the snlcus orbitalis. The cortex is here 

 1"8 mm. in depth. The lamina zonalis extends to a depth of 

 '25 mm., and is succeeded by a very poorly developed lamina 

 granularis externa ; this in turn gives place to the lamina 

 pyraraidalis. The lower aud larger pyramids of the latter 

 form together with the cells of the lamina ganglionaris a zone 

 rich in cells of moderate size, which extends from a depth of 

 "7 mm. to a depth of I'o mm. A faint indication of the lamina 

 granularis interna lying at a distance of about "0 mm. from 

 the surface suggests that only the nppei- Ixjrder of this zone 

 should be reckoned to the lamina pyramidalis, and tluit the 

 greater part of it is derived from the lamina ganglionaris. 

 The lower half millimetre of the cortex is occupied by the 

 lamina multiformis, the greater proportion of the cells of 

 which are of a broad pyramidal form with basal processes 

 extending horizontally. These cells tend to be arranged in 

 horizontal rows, separated by tangentially running bundles 



