714 
MR. W. BEVAN LEWIS ON THE COMPARATIVE 
the cortex in straight or arched direction, within perivascular channels, which in the 
fresh state attain a diameter of *110 mm. In the deeper region of this peripheral zone 
I find a shallow belt of arciform medullated fibres, which originating near the inner 
margin of the peripheral olfactory fasciculus (apparently continuous with the elaustrum) 
is here continued inwards over the whole of the inner olfactory area. 
2 . Granule cell layer .—-These cells forming the involuted layer characterising this 
region attain the average dimensions of 9/x long by 6/x broad, and contain a large oval 
or spheroidal nucleus 6/a in longest diameter. Amongst the cells of this layer we also 
find an abundance of very minute granules scarcely attaining a diameter of 5/x. These 
latter resemble the granules of the modified upper limbic cortex, but are smaller in 
size than these. They are common to the cortex here and to the peculiar medullated 
region which extends as far as the central olfactory fasciculus and anterior commissure, 
and may be regarded as specially the olfactory region of the nucleus caudatus. The 
depth of this region amounts to 3*27 mm., whilst the granule cell formation or second 
layer is *116 mm. deep. 
3. Layer of spindle cells .—Immediately beneath the wavy layer of small angular 
and granule cells lies a formation of fusiform cells, the elements of which attain a 
notable magnitude. Whilst the majority of these cells measure 32/xXl3/x, we 
frequently meet with far larger elements attaining the dimensions of 60/x X 9/x, with 
an oval nucleus 13p, in longest diameter. These spindle cells have their long axes 
parallel to the surface of the cortex, and lie along the course of similarly disposed 
medullated fibres which bend inwards to continue beneath the same layer of the septum 
lucidum. This cortical stratum is therefore essentially an arcuate fasciculus of 
medullated fibres connected with un usually large spindle cells, which bring the cortex 
of the inner olfactory area in connexion with that of the se23tum lucidum and upper 
limbic arc. Beneath the cortical layers above described are the densely aggregated 
olfactory fasciculi, which traverse the deep structure of the olfactory area, and from 
which vertical prolongations descend to the deeper layers of the cortex, probably fusing 
with the arciform medulla.* 
Modified Lower Limbic Type (Plate 50, fig. 6).t 
In the anterior portions of the lower limbic arc and the olfactory lobe, it was stated 
that the cortex was chiefly characterised by the development of the second layer as 
closely appressed clusters of small pyramidal cells, and with the exception of a scanty 
formation of large pyramids, no other nerve-cells are present. The further back we 
examine the lower limbic arc the greater is the development of the larger pyramidal 
cells, until eventually we reach a region where the large cells are much more densely 
grouped. Here, however, a remarkable change has occurred in the second layer, the 
* Diagramaticaily represented in Plate 49, fig. 8, by f. 
| Area covered by this form of cortex is the light shaded portion T to W in figs. 1 and 3. 
