STRUCTURE OF THE CORTEX CEREBRI. 
43 
appearance of the cortex cerebri in Man in or neighbouring upon the motor area cannot 
fail, on examining the cortex of the Pig for the first time, to be struck by one great 
differential character. In Man and the higher Mammalia the cells of the third layer 
increase in size with their depth, so that the lowest stratum consists of tolerably large 
cells, and the eye is thus, as it were, prepared for the enormous elements of the gan¬ 
glionic layer below. In the Pig, however, the transition is most sudden from the 
small cells of the lowest stratum of the third layer to the dense nests of large 
ganglionic cells beneath. The transition is so abrupt as to form a characteristic feature 
in the brain of this group of animals. I will endeavour to give here a general idea of 
this formation by a description of the nerve-elements under the following heads :— 
1. Depth of layer ; 2. Form of cells ; 3. Size of cells ; 4. Processes. 
1. Depth of ganglionic layer. —The pale band corresponding to this layer in Man, 
and containing the large cells grouped in nests or clusters, is in the Pig crowded, with 
very dense groupings of cells in certain regions, whilst at other sites, as above men¬ 
tioned, the laminar or solitary arrangement prevails. The depth of this layer, there¬ 
fore, varies with these two varieties of lamination. In the clustered arrangement the 
average depth is ‘595 mm.; in the laminar arrangement it may be a simple streak of 
cells or attain a depth of from T86 mm. to '372 mm. The greatest depth in the 
clustered regions was ‘697 mm. Further details respecting absolute depth of indi¬ 
vidual layers is given in a tabulated form for convenience of reference. (See p. G2.) 
2. Form of cells. —It has been stated in a former memoir* that a great irregularity 
in marginal conformation is quite peculiar to these cells in Man. Now we can by no 
means state that such is the case with the corresponding elements in the Pig; in fact, 
a striking uniformity in the contour of these cells is observable, by far the greater 
proportion taking the form of an elongate pyramid, the few exceptions occurring being 
usually gigantic spindles. They resemble closely, both in size and form, the large 
pyramidal cells at the deepest portion of the third layer in Bimana, Quadrumana, and 
the large Carnivora, as also the ganglionic cells in the parietal and tempero-sphenoidal 
lobes of Man. Nowhere do we find the irregular, swollen, and at times almost 
globose cells so frequent in the motor area of the human brain. How is it possible, it 
may be asked, to discriminate between these cells and those of the third layer if they 
approach them so closely in size and contour? In the first place, their arrangement 
in nests is indicative of their true significance; in the next place, their abrupt com¬ 
mencement is indicative of a layer distinct from the third ; and, lastly, of still greater 
import to my mind is the fact that in those regions marked by a six-laminated type 
the belt of angular cells becomes interposed between this layer of cells and the third 
layer. To summarise, therefore, we may state that the ganglionic layer in the Pig 
consists of cells which, whilst arranged in clusters corresponding to the nests of Betz 
in the human subject, conform in size and configuration to the lowest pyramidal cells 
of the third layer in Man (Plate 7). 
* Loc . cit . 
G 2 
