32 
BULLETIN OF THE LABORATORIES 
the thalami, which thrust the adjacent ventral wall inward so as al- 
most to fill the cavity. That part of the original cavity which is not 
thus lost is greatly reduced by the adhesion of the dorsal and ventral 
parts of the wall until only a narrow space remains on either side, the 
lateral ventricles. The portion of the lower wall which is invaginated 
appears, when the ventricle is opened, as an arched mass in its floor, 
the cornu ammonis. This lower wall is not simple, but is convoluted, 
forming a folded arch directed cephalad, stretched over the thalamus. 
Thus, imagine that the hollow body [secondary prosencephalic versicle] 
has had the lower wall on either side driven cephalad by a fold springing 
from behind in the direction of the arch of the thalamus opticus (Plate 
III, Fig, 4, a.) By this process there arise a lamina superior and a la- 
mina inferior cornu ammonis (Plate III, Fig. 3, le and li.) The terms 
are strictly applicable in only a part of the course of these bodies, 
since the relation of the two laminae is altered caudad, the upper be- 
coming lateral, the lower median. [These two portions are parts of 
the gyrus fornicatus.] In comparing the Ammon’s horn with other 
parts of the cortex a difference is obvious, especially in the inferior 
lamina, in that a second fold has taken place, intercalating a band of 
smaller cells than those of the remainder between the upper and lower 
laminae. This is the so-called granular layer, or taenia cinerea cornu 
ammonis of Volkmann [gyru> uncinatus, Plate III, Fig 3, The 
two cornua meet and coalesce to some extent in the median line. 
The connection between the two cornua is chiefly due to the confluence 
of the layer of fibres and of large cells of the superior lamina. Far 
cephalad the layers of large and small cells of the inferior lamina also 
coalesce. The fibres arising in the Ammon’s horn of either side arch 
over the thalamus and converge behind the callosum where they separate 
from the cornua and plunge obliquely into that part of the substantia 
cinerea anterior caudad of the collosum and cephalad of the thalamus. 
‘Tn the region of the anterior walls of the third ventricle these grad- 
ually diverging bundles disappear behind the anterior commissure. 
They obviously, therefore, form a longitudinal commissure of the 
anterior ventral part of the hemisphere, the substantia cinerea anterior, 
with the posterior portion of the hemisphere. In other words they 
constitute the fornix.” Stieda recognizes two bundles of fibres in the 
cornu ammonis, one longitudinal, the other transverse, one passing 
to the callosum, the other to the fornix. In carnivora Stieda states 
that the gray matter of the two cornua is not confluent. 
