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The tendency of the convolutions to arrange themselves in parallel curves around the posterior extremity of the fissure of Sylvius was well shown in the brain of a boy of exceedingly low intellect.

These are situated in different parts of the brain and are connected by sub-cortical association tracts, the main pathway of which lies in the vicinity of the upper end of the fissure of Sylvius.

Next we see the optic nerves crossing on the median line, the olfactory nerve, running under the front lobe, which is separated by the fissure of Sylvius from the middle lobe.

S, fissure of Sylvius; M, the medulla; VII, the roots of the facial nerves.

The fissure of Sylvius passed into the fissure of Rolando in one case on both sides, in another on one side only.