STRUCTURE OF THE CORTEX CEREBRI. 
49 
layer. Throughout this layer small pyramidal cells usually measuring 13/x in length 
by 9/x in breadth are found. These latter elements tend in certain regions of the 
brain to accumulate towards the lower half of the third layer; and the pale zone, 
poorly supplied by cells in the anterior extremity of the limbic lobe, becomes in its 
posterior half, and at other sites, occupied by these small pyramidal and angular 
elements which form the fourth layer of the six-laminated cortex. This layer of 
angular elements attains a depth of T86 mm., the cells measuring from 6/x to 9/x 
in greatest length and breadth. Not only do we miss here the gradual increment in 
size of these cells with their greater depth which is so noticeable in Man and the 
Monkey, but we frequently find the largest elements of the series (27/xX 15/x) imme¬ 
diately beneath the second layer. This layer is as a rule richly supplied with cells 
which are densely aggregated. 
Ganglionic layer (Plate 6, D). —This important formation attains a depth of '372 mm. 
below the superimposed stratum. The nerve-cells of this layer vary much in their con¬ 
formation. The most frequent form assumed is that of an elongated pyramid, the apical 
process of which can be traced often as far as the first layer of the cortex. Other cells 
assume the form of elongated spindles, and a frequent form is that of a horned cell, 
which bears a striking resemblance to the egg case of the Skate. The apex process 
may bifurcate close to the cell, giving the latter the form of a horned pyramid, or it 
may divide into two secondary processes of equal diameter at any distance up the third 
layer. The apex process is particularly coarse and does not undergo rapid attenuation. 
The average dimensions of these cells is 46/xXll/x, a measurement which reveals 
clearly the elongated conformation of these elements, in fact, the oval and plump 
rounded contour so frequent in the corresponding cells of Man, the Monkey, and 
the Carnivora is very rarely met with in these animals. Occasionally a larger cell 
than usual is met with, e.g., 65/x X 23/x. They contain an oval nucleus measuring 
13/x in length. These cells are disposed in oval or oblong nests, often covering an 
area 460/x deep by 110/x broad, and contain as many as twenty cells in some situa¬ 
tions. The cells are frequently scattered somewhat irregularly in the anterior portion 
of the limbus, but they become progressively larger and more distinctly nested towards 
the exposed portion of the limbic lobe. The clusters are frequently so closely packed 
as to become confluent, and in many regions on this account the nests are badly 
differentiated. It is impossible after close examination of this formation to arrive at 
any other conclusion than that these cells not only resemble those larger pyramids 
of the third layer in Man in their general form, but also by their gradual increase in 
size from above downwards (the largest cell being invariably lowest in the series) 
claim further affinities to this formation. It is however distinctly differentiated from 
the third layer in the six-laminated regions by the interposition of the layer of small 
angular cells. 
Spindle layer (Plate 6, E).—The lowest formation of the cortex in this region presents 
no special features demanding notice here. The spindle-cells are large in size and the 
MDCCCLXXX. H 
