316 DR. G. ELLIOT SMITH OiN" 



breadth : in other words, an increasing area of that part of the fascia dentata which is in 

 contact Avith tlie cortex {ride figure 20) becomes exposed. Pari passu with this un- 

 covering of the fascia dentata, the opposed surfaces of pallium and hippocampus, which hide 

 it from view elsewhere, also hecome exposed. There is a general unrolling, as it were, 

 of the hippocanipal formation. So that, as the fascia dentata becomes more and more 

 exposed, we also find that the hippocampo-pallial junction approaches and ultimately 

 appears upon the surface as a shallow furrow separ-ating the pallium, which lies behind 

 it, from the exjjosed surface of the hippocampus, which now makes its appearance on the 

 surface in front of the furrow (fig. 21, x). 



This exjwsed lup]iocampus {/dppocampus nuchis) is the true morphological surface of 

 the hippocampus which elsewhere is submerged, hidden in the depths of the hipjiocampal 

 fissure *. Near the mesial j)lane it appears to emerge from the hippocampal fissure, and 

 under the name " Ballenioiiidung ," which Zuckerkandl introduced, it has given rise to 

 much discussion. Zuckerkandl's " Ealkeuwiudung " is nothing else than our '■'■ hippo- 

 campus nndusr 



As the fascia dentata becomes more ex2:)0sed and apparently broader it bends trans- 

 versely inward, and when quite close to the mesial plane it bends suddenly backward and 

 rapidly tapers to a point l)elow the splenium of tlie corpus callosum. These recurved 

 portions of the fascise dentatte upon the two sides of the mesial plane are in close 

 proximity the one to the other, and in many animals [c. (j. the Rabbit) they actually 

 meet and fuse in the course of development f . But the two structures arc development- 

 ally independent, and each is derived w holly from its own cerebral hemis2)here. 



If we now return to the consideration of the mesial surface of the hemisphere (fig. 4), 

 we readily recognize the mesial border of this infrasplenial bent part of the fascia dentata 

 as a pear-shaped body proceeding backward upon the imder surface of the psalterium 

 dorsale and splenium, and appearing to be directly continued around the splenium on to the 

 dorsal surface of the corpus callosum as a rovmded white cord. But the fascia dentata 

 really ceases, as a definitely recognizable entity, upon the ventral surface of the splenium. 

 The rounded white cord which surrovmds the splenium, and a2)pcars to be merely the 

 attenuated fascia dentata, is more directly the upwai-d continuation of the hippocampus 

 iiudus, i. e. the hippocampus proper. 



The fascia dentata, as its mode of develojiment indicates, is a comparatively late 

 specialization of the margin of the hipjiocampus projier. As it develops it rolls itself, 

 as it were, over the surface of the hippocampus and hides this from view. On the 

 inferior aspect of the splenium the hippocampal formation unrolls, the hippocampus 

 proper becomes once more exposed, the fascia dentata tapers and disappears almost 

 entirely, and a remnant of the more primitive liif)pocampus proper surrounds the 

 splenium and extends along the whole length of the upper surface of the corj)us callosum 

 as a rounded w^hite cord. 



This cord-like remnant is a vestige of the anterior part of the more extensive hippo- 



* The true significance of this will be appreciated at a glance from fig. 21 of my short memoir in the ' Journal of 

 Anatomy and Physiology,' vol. xxsii. p. 49. 



t Compare in this connection the comparative observations of Stieda in Zeitsch. f. wisscnsch. Zoologie, 1870. 



