If now the medial surface of the hemisphere, which forms one side of the longitudinal fissure, be examined, there is seen a large convolution running just above and parallel with the corpus callosum. It is called the gyrus cinguli (fornicatus). Below and separating it from the corpus callosum is the callosal fissure; above it is the calloso-marginal fissure. The convolution above the latter, forming the margin of the hemisphere, is the marginal convolution. The callosomarginal fissure at its posterior portion turns upward and ends on the margin of the hemisphere, just posterior to the fissure of Rolando, or central fissure, and serves to identify it. This marks the posterior limit of the frontal lobe. The posterior end of the frontal lobe surrounds the upper end of the central fissure and on that account is called the paracentral lobule. Its anterior boundary is marked by the paracentral fissure, or sulcus. Between the callosomarginal fissure in front and the parieto-occipital fissure behind is the parietal lobe, called, from its square shape on the medial surface, the quadrate lobule, or from being anterior to the cuneus lobule, the precuneus. Running downward and backward from the deeper portion of the paneto-occipital fissure is a very distinct depression called the calcarine fissure. These two fissures include a wedge-shaped piece of the occipital lobe called, from its shape, the cuneus lobule. It is of interest in reference to the sense of sight.

Fig. 42.   Gyri, sulci, and fissures of the medial surface of the cerebral hemisphere.

Fig. 42. - Gyri, sulci, and fissures of the medial surface of the cerebral hemisphere.