514 WILLIAM H. F. ADDISON 
hippocampus. As there were no cell-preparations available for 
study, one can say nothing of the cell-layers, but one can readily 
appreciate the simple atypical form of the hippocampus, and its 
small size, which produces no apparent bulging into the ventricle. 
There is a very shallow fissura hippocampi, below which, in figure 
8, there is seen a small cortical area of the gyrus hippocampi, 
containing superficially a layer of fine medullated nerve fibers. 
This small cortical area is evidently the representative of the 
subiculum. There is no separated gyrus dentatus but above the 
fissura hippocampi are clusters of cells, which may represent 
the remnants of the gyrus dentatus. At the apex of the whole 
formation proceeds the fimbria in the typical way. Descriptions 
of the outer appearance of the hippocampus are to be found in 
Proca (’79), Zuckerkandl (’87) and Elliot Smith (02). 
The fimbria arises as a narrow elongated bundle from the 
margin of the hippocampus (figs. 7 and 8). Part of its fibers 
cross soon to the opposite side forming the hippocampal commis- 
sure, commissura dorsalis, or psalterium. This is shown as a 
_ rather broad band of fibers in figure 9, lying ventral to the cor- 
pus callosum, and consisting of fibers which stain more lightly 
than those of the corpus callosum. The psalterium appears so 
well developed that the possibility is suggested that it may con- 
tain other fibers in addition to the commissural hippocampal 
fibers. Perhaps fibers coming from the parolfactory cortex 
may cross here to reach the opposite hippocampus. <A small 
portion of the psalterium is still apparent in section 153 (fig. 11). 
Other fibers of the fimbria proceed uncrossed as two flattened 
bands of the crura fornicis (section 169, fig. 12). These approach 
one another in the midline (section 181, fig. 13), where they form 
the body of the fornix. The general course of the fornix fibers 
is shown in figure 15, as reconstructed from several consecutive 
sagittal sections. The fornix fibers proceed under the corpus 
callosum until they enter the margin of the septum pellucidum 
(figs. 13 and14). They traverse its curved outline and so are cut 
across twice in figure 13. They are seen again in figure 12, in the 
most anterior and ventral portion of the septum pellucidum. 
In our series of sections cut as shown in figure 6, we were unable 
