STRUCTURE OF THE CORTEX CEREBRI. 
4 1 
five to six cells, which groups are invariably distant from one another. Their 
maximum dimensions are obtained at B ( = 40 /a X 2L/x) and at F (= 37/x X 2 7f), the 
minimum atE (= 28/x X 18/a). 
Carrying our observations into the structure of the upper parietal region, imme¬ 
diately above the inter-parietal fissure, we find the solitary or laminar type of the 
ganglionic layer as most prevalent throughout. We have here, of course, two convolu¬ 
tions to deal with, viz.: the third parietal and the fourth or sagittal convolution. The 
anterior extremities of these gyri exhibit, as above stated, certain modifications in the 
immediate neighbourhood of the crucial and inter-parietal sulci; but with this exception 
the laminar arrangement is maintained. In the regions alluded to, the nested cells 
may be traced from the crucial and inter-parietal sulci some distance up the adjacent 
side of the upper parietal convolutions. They frequently reach the summit of these 
gyri as extremely rich nests, which are invariably discrete and often very distant. 
The laminar arrangement of the posterior parietal region is highly characteristic. It 
appears as a pale band, along the upper limit of which a line of solitary cells lie at 
distances of from ’139 mm. to '379 mm. apart. Frequently, however, two or three 
of such cells ajipear side by side. In this region we recognise the tendency to the 
accumulation of angular and small pyramidal elements towards the lower limits of 
the third layer, which tendency becomes more marked the further back we carry our 
examination of the cortex. It must, however, be distinctly understood that we have 
here no distinct belt of small angular elements ; no accumulation of cells so differentiated 
from the third and subjacent layers as to merit the name of an additional layer of the 
cortex. We find over the greater portion of the parietal region but the faint shadow¬ 
ing forth of the six-laminated type—an arrangement met with over a very limited 
region of the cortex in this animal. 
The Cortex Cerebri of the Sheep. 
The points of resemblance exhibited between the cortex of the Sheep and the Pig 
are so numerous that to describe the structure in each separate lobe of the Sheep’s 
brain would be to a great extent a task of recapitulation. I shall therefore content 
myself with a description of the structure of the cortex in that great fundamental 
portion of the brain—the limbic lobe, and emphasise more especially those features 
where points of divergence are indicated. 
Lamination of the great limbic lobe .—We have here in the anterior portions of 
the upper arc to deal with a five-laminated cortex over an area which, as will be 
pointed out further on, is coextensive with the same formation in the Pig. 
First layer (Plate 6, A).—The average depth of this pale stratum is '550 mm. It 
embraces the two forms of nucleated cells which are found in this layer in other animals, 
viz.: the perivascular and neuroglia corpuscles, measuring 5/a and 9/x in diameter. These 
cells contain large nuclei. Immediately beneath the pia mater great numbers of the 
