720 
MB. W. BE VAN LEWIS ON THE COMPARATIVE 
cells—a wealth, demonstrated both in depth of stratum and close aggregation of its 
constituents. 
The Cornu Ammonis (Plate 49, fig. 7). 
Peripheral cortical zone. —In the cornu ammonis this stratum may be readily seen 
to consist of a superficial and deeper region, which by Meynert and others have been 
regarded (in the human brain) as two distinct laminae, representative of the first and 
second cortical layers elsewhere. But whereas the second layer of superficial angular 
cells is not developed in the Babbit, the lower portion of this zone can scarcely be 
regarded as representative of a series of cells which do not appear in the most complex 
regions of the cortex in this animal. These two divisions have been named the nuclear 
and lacunar layers—the latter also termed by Kupffer the stratum reticulare. On 
close examination of this inner or reticulated structure it becomes apparent that it 
clearly corresponds to the deeper portion of the peripheral zone of other cortical regions. 
In diverse realms of the cerebral cortex it was stated that this peripheral zone in various 
animals exhibited two clearly distinct portions—the outer or more superficial being 
often distinguished by a layer of horizontally disposed medullated fibres following the 
various involutions of the cortex and parallel to the surface, and extending often to a 
depth of one-third or even one-half that of the first layer. Now this peripheral 
stratum appears as the representative of the nuclear layer of the cornu ammonis. The 
inner or deeper portion of this zone elsewhere was seen to be composed of a dense 
network, formed by the apex processes of the subjacent cells dividing and subdividing 
in their course upwards. This was found to be the case in the Cat, Sheep, Pig, and 
Babbit. In the cornu ammonis the same network is apparent, but being here entirely 
constituted by the apex processes of much larger cells—the ganglionic cells—it is a 
coarser and far more prominent formation. The whole depth of this peripheral zone is 
on an average *836 mm., the outer medullated layer being about ‘511 mm. The 
nuclear lamina, or as I prefer to term it, the medullated division of the peripheral 
zone, includes the following constituent elements :— 
a. Band of medullated fibres derived from re-union of meshwork of the divided 
apical processes of ganglionic cells. 
h. Numerous large blood-vessels. 
c. A neuroglia matrix, containing a profusion of the ordinary nucleated connective 
cell; also the Deiter’s corpuscle and perivascular nuclei. 
d. Spindle-form cells. 
Of these constituent elements the blood-vessels are large, and dip through the 
medullated portion from the investing pia mater into the deeper division of the 
peripheral zone. Here they divide into a series of anastomosing branches, which, with 
the meshwork of nerve processes, gives this region its characteristic reticulated aspect. 
