Inferior Surface of Brain

Posterior Medial Surface. The posterior part of the medial surface has two deep sulci. The upper parietooccipital sulcus inclines backward and upward to cut the superior border. The lower calcarine sulcus extends forward from the occipital pole to end beneath the splenium of the corpus callosum, and the isthmus of cortex between them connects the cingulate and parahippocampal gyri. The wedge-shaped region between the parietooccipital and calcarine sulci is the cuneus, while the area between the parietooccipital sulcus and the paracentral lobule is the precuneus. The main visuosensory area is located in the walls of the calcarine sulcus and in the adjacent cortex.

INFERIOR SURFACE OF CEREBRAL HEMISPHERE

The inferior surface is divided by the stem of the lateral sulcus into smaller, orbital and larger, tentorial surfaces.

The orbital surface rests on the roofs of the orbit and nose and is marked by an H-shaped orbital sulcus, as well as by a straight groove on the medial side, the olfactory sulcus, which lodges the olfactory bulb and tract. The orbital sulcus demarcates the orbital gyri; the small convolution medial to the olfactory sulcus is the straight gyrus.

The tentorial surface lies partly on the floor of the middle cranial fossa and partly on the tentorium cerebelli. It has two anteroposterior grooves, the collateral and occipitotemporal sulci. Both run almost directly forward from the occipital pole to the temporal pole; like other sulci, they may be subdivided, and the anterior end of the collateral sulcus is called the rhinal sulcus. The parahippocampal and lingual gyri lie medial to the collateral sulcus. The dentate gyrus, a narrow fringe of cortex with transverse markings, occupies the groove between the parahippocampal gyrus and the fimbria of the hippocampus. The anterior end of the parahippocampal gyrus becomes recurved to form the uncus, which is partly occupied by the cortical olfactory area. The medial occipitotemporal gyrus is fusiform in shape, and lies between the collateral and occipitotemporal sulci. The lateral occipitotemporal gyrus lies lateral to the occipitotemporal sulcus and is continuous with the inferior temporal gyrus around the inferior margin of the hemisphere.