OF DENISON UNIVERSITY. 
83 
is not direct along the very mesal line, but here the tela is distended 
to form a homologue of the dorsal sac of fishes which extend caudad 
to the epiphysis and is distinct from the aula except along the median 
line. Its walls give rise to abundant plexus. (2) The hippocampal 
commissure and fornix body form an oval mass dorsad of the anterior 
commissure and are. attached to it. From the lateral aspects of the for- 
nix body cephalo-ventrad the descending fornix tracts appear. In exact- 
ly median sections the fornix body is circumscribed on all sides except 
ventrad by the ventricle, while the tela springs from a special promi- 
nence, but laterad the tela adheres to the fornix body and can be 
traced to the free margin of the fascia dentata (gyrus uncinatus). (3) 
The anterior commissure itself is obscurely composed of three portions 
which are medianly rolled into a compact cylinder. Each has a sheath 
which can be seen under favorable circumstances. The dorsal and 
ventral parts are crescentic in section, while the median portion is 
oval. The dorsal crescent overlaps the ventral cephalad. (4) The 
lamina terminalis is medianly very thin but contains some gray mat- 
ter. (5) The callosal fibres are too few to be very obvious in this 
view. 
Dorsal and Ventral regions of the Cerebnm. We think there are 
good morphological and practical reasons for distinguishing the dorsal 
and ventral portions of the cerebrum as structures essentially distinct. 
The limits of the two regions are easily drawn in the opossum. Ce- 
phalad the olfactory crus with its cortexjis very sharply distinguished 
from the pre-crucial portion dorsad of it. (Plate A, Fig. 2.) Here 
the cortex of the ventral portion is very largely covered by the olfac- 
tory fibres. Laterad, the two regions are limited, as we proceed caud- 
ad, by the rhinalis fissure, mesad the splenial fissure is an equally dis- 
tinct boundary. Cephalad, these two fissures occupy nearly the same 
horizontal plane but caudad the former passes ventrad and the latter 
dorsad, a change which may be ascribed to the interposition of the 
thalamus. The ventral portion is distinct in cellular structure and 
presumably in function from the dorsal region. In the former two 
prominences have their origin, the pyriform lobe of either side caudad. 
and the post-rhinal lobe cephalad. At the mesal union of the ventral and 
dorsal regions the hippocampus has its origin as a curious convolution 
at the splenial fissure. The hippocampus has been carefully described 
in rodents by C. Judson Herrick in Bulletin Denison Univ. Vol. 
VI. The relations are still more simple in marsupials and, because 
