122 
verse section through this formation in the region indicated above (i. e. 
in front of the commissures) the hippocampus may be seen to form the 
dorso-mesial angle of the hemisphere. The appearance of this region 
in the black snake (Pseudechis) is represented in a purely schematic 
manner in Figure 1. 
Hippocampus 
Fig. 1. Scheme of 
hippocampal formation of 
_ a Reptile (Pseudechis) 
Fascia dentata }- m: ; 
as seen In transverse sec- 
tion in front of the region 
of the commissures. 
Upon tracing it downwards upon the mesial wall of the hemi- 
sphere, the characteristic histological structure of the hippocampus 
will be found to cease abruptly and give place to the precommissural 
area, from which it is separated by the fornix fibres. Throughout this 
- simple hippocampus consists of four layers: 1) a thin white medullary 
layer next to the ventricle — the so-called alveus; 2) a layer of 
scattered polymorphous cells; 3) a very regular lamina of closely packed 
cells and 4) the molecular layer. 
The third layer (3) on the dorsal aspect of the brain consists of 
large pyramidal cells, with large cell bodies. As it is traced on to 
the mesial aspect these large cells gradually [in fig. 1. the change is 
represented as abrupt] give place to a dense mass of smaller and 
more closely packed cells, so-called “granules”. The latter constitute 
the stratum granulosum of the Fascia dentata; while the pyramidal 
cells are the homologues of the “layer of pyramids of the cornu Am- 
monis — the lamina grigia circonvoluta” of Goer). 
Although Sprrzka ?) and Epincer 3) have located the hippocampus 
1) loc. cit. 
2) Journal of nervous and mental Diseases, 1880, and Science, 1880 — 
quoted by Britt (vide infra) and Strasser (loc. cit.). 
3) “Riechapparat und,Ammonshorn”. Anatomischer Anzeiger, Jahrg. 
VIII, No. 10, 8. April 1893. 
