STRUCTURE OF THE LOBES OF THE CEREBRUM. 395 



It is only in regard to its coarser features that the cornu 

 Ammonis presents a more complicated structure than other 

 convolutions; but in regard to its textural lamination and 

 the types of its cells, it is the simplest of the cerebral con- 

 volutions : in fact, a defective structure, including the pyramidal 

 cell-forms alone of all those that are found in other parts of 

 the cortex. 



The cortex in the subiculum is composed exclusively of 

 small and large pyramidal cells. And whilst here, on account 

 of the absence of the fusiform cells, one form of central con- 

 nection of the association systems fails, yet the other form of 

 connection that occurs between the cortical regions, formed by 

 the white substance of the membrana alba involvens, else- 

 where scantily developed, is, by way of compensation strongly 

 developed in the substantia reticularis. The external contour 

 of the second cortical layer of the cerebrum appears, therefore, 

 fenestrated (interrupted) (fig. 236, $), in consequence of the 

 passage of fasciculi, of the apical processes (admitted even by 

 Arndtto be branched) of the large pyramidal cells, which furnish 

 their contingent to the formatio reticularis. The involutedl&yQY 

 (ccc) in the interior of the proper cornu Ammonis consists 

 exclusively of the largest forms, and therefore of the pyramidal 

 cells of the inner half of the third layer of the cortex. Lastly, 

 in the region of the fascia dentata the small forms of cells 

 recur closely compressed in a manner peculiar to this tissue 

 (forming the stratum corporum nerveorum artorum), whilst in 

 the other parts of the cortex they preserve a mean distance 

 of 100 n from one another. It is to this close arrangement 

 that we must attribute the fact that Kupffer, Kolliker, and 

 Deiters have overlooked the delicate and hazy-outlined proto- 

 plasm surrounding them, and have only noted the presence 

 of vesicular nuclei. Hence the connective-tissue layer, stratum 

 granulosum, which they admit, has no existence, and has 

 been rightly regarded by Arndt as composed of nerve cells. 

 Into the laminated structure of the cornu Ammonis, which is 

 poor in nerve corpuscles, the whole thickness of the non-nervous 

 matrix is thus introduced, producing the lamination schematic-* 

 ally represented in fig. 237 (which should be compared with that 

 of fig. 236). Following in the latter figure the external contour 



