The inferior frontal convolution winds around the ascending branch of the fissure of Sylvius, in the anterior and inferior portion of the cerebrum. Parietal Lobe.-The ascending parietal convolution is situated just behind the fissure of Rolando, running downward and forward; above, it becomes continuous with the upper parietal convolution, and below, winds around to be united with the ascending frontal. DIAGRAM SHOWING FISSURES AND CONVOLUTIONS OF THE LEFT SIDE OF THE HUMAN F. Frontal. P. Parietal. O. Occipital. T. Temporo-sphenoidal lobe. S. Fissure of Sylvius. S'. Horizontal. S". Ascending ramus of S. c. Sulcus centralis, or fissure of Rolando. A. Ascending frontal, and B. ascending parietal, convolution. F1. Superior. F2. Middle, and F. Inferior frontal convolutions. f. Superior, f. Inferior, frontal fissures. fg. Sulcus præcentralis. P. Superior parietal lobule. P2. Inferior parietal lobule, consisting of P2, supra-marginal gyrus, and P'2, angular gyrus. ip. Sulcus interparietalis. cm. Termination of calloso-marginal fissure. 01. First, O2, second, Og, third, occipital convolutions. o. Parieto-occipital fissure. 0. Transverse occipital fissure. 02 Inferior longitudinal occipital fissure. T1, first, T2, second, T3, temporo-sphenoidal, convolutions. t1, first, to, second, temporo-sphenoidal fissures.-Landois' Physiology. The upper parietal convolution is situated between the parietal and longitudinal fissures. The supra-marginal convolution winds around the superior extremity of the fissure of Sylvius. The angular convolution, a continuation of the preceding, follows the parietal fissure to its posterior extremity, and then makes a sharp angle downward and forward. Temporo-sphenoidal Lobe.-Contains three well marked convolutions, the superior, middle, and inferior, separated by well-defined fissures, and continuous posteriorly with the convolutions of the parietal lobe. The Occipital Lobe lies behind the parieto-occipital fissure, and contains the superior, middle, and inferior convolutions, not well marked. The central lobe, or island of Reil, situated at the bifurcation of the fissure of Sylvius, is a triangular-shaped cluster of six convolutions, the gyri operti, which are connected with those of the frontal, parietal, and temporo-sphenoidal lobes. Upon the inner or mesial aspect of the hemisphere are found (Fig. 15)— 1. The paracentral lobule, lying in the region of the upper extremity of the fissure of Rolando; it contains the large giant cells of Betz. Injury to this convolution is followed by degeneration of the motor tract. 2. The gyrus fornicatus, lying below the calloso-marginal fissure. Running parallel with the corpus callosum, it terminates at its posterior border in the hippocampal gyrus. 3. The gyrus hippocampus (H) is formed by the union of the preceding convolution with the occipito-temporal. It runs forward and terminates in a hooked extremity—uncus. 4. The quadrate lobule or precuneus lies between the upper extremity of the calloso-marginal fissure and the parieto-occipital. 5. The cuneus lies posteriorly to the quadrate lobule. It is a wedgeshaped mass enclosed by the calcarine and parieto-occipital fissures. Structure. The gray matter of the cerebrum, about one-eighth of an inch thick, is composed of five layers of nerve cells: (1) a superficial layer, containing a few small multipolar ganglion cells; (2) small ganglion cells, pyramidal in shape; (3) a layer of large pyramidal ganglion cells with processes running off superiorly and laterally; (4) the granular formation containing nerve cells; (5) spindle-shaped and branching nerve cells of moderate size. The white matter consists of three distinct sets of fibers : 1. The diverging or peduncular fibers are mainly derived from the |