84 
BULLETIN OF THE LABORATORIES 
of the absence of the callosum, they may serve as a type for compari- 
son. Beginning at a region cephalad of the union of the two hemi- 
spheres (Plate A, Fig. 3.) we observe that the cortex at the splenial 
fissure becomes very narrow and dense and the cells acquire much the 
appearance of those of the hippocampus. The outer neuroglia layer is 
thickened and the peripheral fibre zone is collected in small tracts. 
These tracts, some of the fibres of which may represent the mesal 
olfactory tract, are thus described in my notes. ‘‘A tract which 
arises ventro-mesal near the crus of the olfactory (exact locality inde- 
terminate) passes caudo-dorsad within the cortex. The several small 
bundles emerge into the neuroglia zone and before the formation of a 
deep splenial fissure have attained a position dorsad to it. Thence 
they pass caudad and are carried entad by the deepening of the 
fissure and are last seen in the region of the anterior commissure ap- 
parently terminating in cells of the uncinate gyrus.” 
Entad, a strong tract derived from the cells of this region passes 
meso-ventrad of the tract mentioned, is separated from the corpus stri- 
atum by a spur of the ventricle, and is filled with thickly scattered cells. 
An oblique band of cells passes from the ventricle ventrad toward the 
meson and seems a continuation of the irregular chain of cell-clusters 
characteristic of the pseudo-cortex of the ventral region. On the oth- 
er side of the ventricle opposite the dorsal end of this cell-series is the 
cephalic branch of the anterior commissure. The limits of the gyrus 
fornicatus and uncinatus are more or less arbitrarily determined in 
mammalia. Ranney considers the posterior margin or splenium of 
the callosum the point where the former passes into the latter. In the 
present case, however, there being no such guide, we are forced to de- 
pend upon morphological modifications of the organs themselves. 
The gyrus fornicatus arises cephalad by the fold induced by the sple- 
nial fissure already described. It may be traced cephalad nearly to the 
olfactory. The uncinate gyrus is a second fold which appears as the 
two hemispheres fuse. (Plate A, Fig. 4.) The free dorsal margin is 
outwardly folded and at the same time ‘Taulted” by being slid some- 
what laterad as if by the agency of the thalamus wedged between the 
hemispheres. The fornicate and uncinate gyri are curved in opposite 
senses and related to each other somewhat as are tiles on a roof. In 
speaking of the uncinate gyrus as the free portion of the median cor- 
tex it must be understood in a limited sense, for the mesal margin 
passes into the plexus and tela and ultimately forms the connection 
