THE CEREBRAL CORTEX 77 



sweep around the free extremity of gray matter, and thus arrive upon its surface, there passing 

 beneath the layer of epithelium. Hence the layer of white matter which we have described 

 as the second layer of the hippocampus is really made up not only of the neuraxons issuing 

 directly into it from the first set of pyramids described, but also contains fibres coming from 

 the second set of pyramids by a long spiral curve. 



It is possible in the plate to follow the layer of pyramids all the way around the curve 

 of the cortical fold, and thus to become convinced that this layer of pyramids is really a single 

 layer folded upon itself, and hence necessarily lying with all the bases outward. 



Plate LII. shows a section through the hippocampus at a higher power. At the bottom 

 of the plate the layer of white substance is seen, with a few fibres passing chiefly in a 

 horizontal direction. Above this layer the pyramids lie with their long apical processes, 

 similar in appearance to those which we have already studied. These apical processes are 

 seen to divide and enter the layer of fine fibres, where they interlace with the fine horizontal 

 fibres of the superficial layer of the cortex. These fine fibres are quite easily visible in 

 the plates. In the ordinary cortex the superficial layer is comparatively thin, and the apical 

 processes of the pyramids diverge and become parallel with the surface soon after their entrance 

 into it; but in this region it is evident that the layer of tangential fibres is broad, and that 

 there is less tendency of the apical processes to become horizontal. The interlacing of the 

 two sets of fibres in this layer is well demonstrated in the plate. In the plate a few small 

 cells can be seen in the superficial layer. These have been termed stellate cells by Cajal. 

 They have numerous dendrites which branch and interlace with the other fibres of this layer 

 adding to its complexity. Dejerine 1 describes other fibres entering and branching in this layer 

 which are terminal collaterals from the cells of the other layers. It will be noticed that no 

 distinction has been made between the layer of small pyramids and the layer of large pyra- 

 mids in this description of the hippocampus. No such distinction is possible, because the 

 cells are intermingled. 



1 Anatomie des Centres Nerveux, p. 722. Paris. 1895. 



