754 
MR. A. SANDERS ON THE ANATOMY OF THE 
ridges of a somewhat triangular shape projecting into the ventricle of the optic lobe, 
and are placed along the inner and contiguous margins of the two halves of the 
tectum. The border of each ridge, which is turned towards the ventricle, is lined by 
a delicate layer of columnar epithelial cells, which lie immediately upon the nervous 
elements, without the intervention of any connective tissue. 
The cells (fig. 19) which constitute the fornix are mostly of a spherical form, 
consisting almost entirely of nuclei with only a narrow rim of protoplasm round them ; 
they generally contain a spot-like nucleolus ; they usually measure 0'003 millim. or 
0 - 004 millim, in diameter. Occasionally larger cells occur, which present a triangular 
shape from the greater quantity of protoplasm belonging to them. One of these is 
seen in the figure. These cells are arranged in rows, or in single tiles radiating from 
the upper and inner angle of the fornix ; each row is separated from its neighbour 
by bundles of fibrillm, which also radiate from the same point ; these bundles are 
thicker at the proximal end, and gradually become smaller by giving off radiating 
fibrils in then - course. The cells are attached to these fibrils sometimes by short 
branchlets, and sometimes they are sessile. The fornix forms a link connecting 
the sixth layer of the tectum to the granular layer of the valvula cerebelli, by 
which they are further continuous with the third layer in the cerebellum. 
T ori Semicirculares. 
The tori semicirculares (fig. 20, a.) may be considered as the anterior termination of 
the medulla oblongata ; they are tuberosities of a more or less semicircular shape, 
which project into the floor of the ventricle of the optic lobe ; they are principally 
composed of grey matter, through which the bundles of the crura lobi optici pass on their 
way to the internal surface of the tectum lobi optici. The surface turned towards the 
ventricle is lined by a stratum of connective tissue (fig. 20, ep.), which is continuous with 
the corresponding lining of the tectum ; its margin is bordered by a layer of columnar 
epithelial cells, the internally directed extremities of which pass into and form the 
fibrilke of the connective tissue, as in the seventh layer of the tectum. This appears 
to correspond to the “ependyma ventriculorum.” The principal characteristics of the 
tori semicirculares are small cells (fig. 20, b.), elongated, narrow, and tapering at their 
pointed extremities into long fibres, which can be traced th rough the substance of the 
torus to the level of the bundles of nerve-fibres which belong to the crura lobi optici ; 
they have a circular or oval nucleus which usually occupies the whole width of the thickest 
part of the cell ; the nucleolus is generally represented by a few granules. They vary 
in length from 0’009 millim. to 0'016 millim., and in width from 0‘004 millim. to 
O'OOG millim. ; they are arranged in a row along the margin of the torus, and in the 
interior there are two or three, more or less complete, nearly horizontal rows of the 
same species of cells. The deeper part of this tuberosity is occupied by bundles of 
nerve-fibres belonging to the crura lobi optici, which pass through them on their way 
