OF DENISON UNIVERSITY. 33 



Reference to Plate III will render these statements of Stieda clear 

 in spite of the condensed form in which they are necessarily presented. 

 The first fold mentioned by him, the primary fold of the hippocampus 

 (Plate III, a,) does not appear in transverse sections to be a mere fold, 

 or fissure, springing from behind; but it is complicated by the fact 

 that its dorsal portion is pushed much farther cephalad than its ven- 

 tral. The latter only passe's as far as the level of the corpus mam- 

 millare (Figs. 3 and 4.) Cephalad of this region the lamina next the 

 the lateral ventricle, which I have called lamina ectalis (the superior 

 lamina of Stieda, Fig. 3, le,) is in direct continuity ventrally with the 

 other, the lamina entalis (or lamina inferior of Stieda, Fig. 3, li.) The 

 fact that the dorsal portion of the primary fold of the hippocampus 

 appears in transverse sections to pass much farther cephalad than the 

 ventral portion is due to the arched form of the hippocampus itself. 

 By reason of this forward arch the caudal portion of the hippocampus 

 appears in longitundinal section, the cephalic portion in transverse 

 section in these figures. The laminae ectalis and entalis together con- 

 stitute the gyrus fornicatus. By means of this primary fold the hippo- 

 campus is pushed far cephalad under the callosum beyond the chiasm 

 until it comes into direct continuity with the fornix body in the region 

 of the lamina terminalis. The primary fold reaches almost to the>end 

 of the gyrus fornicatus, but in Fig. 1 has disappeared. 



The true relations of the gyrus uncinatus are much more diffi- 

 cult to make out. It is formed, as Stieda says, by a secondary fold of 

 the gyrus fornicatus; but it is not, like the primary fold, due to an in- 

 vagination, or convolution. It is rather a reflected portion of the 

 margin of the lamina entalis. This margin is folded back upon itself, 

 the folded portion, i. e. the gyrus uncinatus, being reflexed ventrad 

 and cephalad, so that the free margin of the latter lies next to the 

 diencephalon and mesencephalon. The convexity of the fold is di- 

 rected cephalad, and toward the caudal end of the hippocampus it 

 apparently in transverse sections increases greatly in size. This ap- 

 pearance, however, is due to the arched character of the hippocampus 

 by which the caudal portion is seen in longitudinal section, as above 

 alluded to. That the gyrus uncinatus is a true fold from the gyrus 

 fornicatus is not very obvious from these sections, since the gray mat- 

 ter of the two gyri is nowhere in direct continuity. Moreover the cell 

 structure is essentially different, the gyrus fornicatus having typical 

 flask-cells, but the gyrus uncinatus smaller deeply staining cells which 



