420 J. B. JOHNSTON 
be described as part of the general pallium. The area of loose 
cells probably belongs to the hippocampal formation and the 
transitional region called the subiculum. 
As transverse sections are followed caudad the area which is 
here assigned to hippocampal formation and subiculum grows 
rapidly wider. There is nowhere a sharp line of demarcation 
between hippocampus and general pallium, and none is to be 
expected. There is everywhere noticeable the point at which 
the deep cell layer becomes abruptly more compact. This point 
has been taken as the medial boundary of the general pallium 
in making the model so that what is there shown as hippocampal 
formation probably includes the equivalent of the subiculum as 
well (see fig. 6). 
As the sections are traced caudad there is a gradual change in 
the size of the cells. The cells of the hippocampal formation 
become smaller, those of the dorsal general pallium somewhat 
larger, until the difference is at first noticeable, then conspicuous. 
From the level of the commissures caudad the cells of the hippo- 
campus are much smaller than those of the general cortex. 
In the occipital and temporal poles of the hemisphere essenti- 
ally the same characters are found. Near the fimbria border is 
an area of dense cells in a deep layer. Next to it is an area with 
cells loosely arranged and many of them near the periphery (fig. 
45). Inthe temporal region this area of ldose cells is narrow and 
is accompanied by an internal sulcus which serves as an addi- 
tional landmark. The boundary shown in the model made from 
transverse sections has been carefully checked up by means of 
horizontal sections and found to be essentially correct. 
The fimbria passes over the interventricular foramen and con- 
tinues back along the border of the hippocampal formation to 
which the choroid plexus is attached (fig. 57). The bundle 
decreases in size as it proceeds but is still fairly large at the 
caudal end of the choroid fissure. Here the fimbria bends 
around the end of the fissure and spreads in the medial wall of 
the ventricle medial to the position of the large-celled amyg- 
daloid nucleus. This is sufficient evidence that the hippocampal 
formation extends around the end of the choroid fissure into the 
