If the reader has not fully mastered the intricacy of the brain structure, he will find his difficulties removed by studying two more skilful dissections. The following engraving presents the appearances when we cut through the middle of the brain horizontally and reveal the bottom of the ventricles, in which we see the great ganglion, or optic thalamus and corpus striatum, and the three localities at which the hemispheres are connected by fibres on the median line, called anterior, middle, and posterior commissures. These commissures are of no importance in our study; they assist the corpus callosum in maintaining a close connection between the right and left hemispheres.