Cerebral Lobes - Telencephalon

Cerebral Lobes

The hemisphere is divided into four cerebral lobes:

The frontal lobe (red)

!   The parietal lobe (light blue)

!   The temporal lobe (dark blue)

!   The occipital lobe (purple)

The hemispheric surface consists of grooves, or sulci, and convolutions, or gyri. We distin-guish primary, secondary, and tertiary sulci. The primary sulci appear first and are equally well developed in all human brains (central sulcus, calcarine sulcus). The sec-ondary sulci are variable. The tertiary sulci appear last, being irregular and different in each brain. Thus, each brain has its own sur-face relief as an expression of individuality, like the features of the face.

The frontal lobe extends from the frontalpole (AC1) to thecentral sulcus(AB2), whichtogether with the precentral sulcus (A3) de-fines the precentral gyrus (A4). The latter is grouped with the postcentral gyrus (A5) to form the central region, which spreads be-yond the edge of the hemisphere (AB6) to the paracentral gyrus (B7). Furthermore, thefrontal lobe exhibits three major convolu-tions: the superior frontal gyrus (A8), the middle frontal gyrus (A9), and theinferior frontal gyrus (A10); they are separated bythe superior frontal sulcus (A11) and the in-ferior frontal sulcus (A12). Three parts aredistinguished at the inferior frontal gyrus that define the lateral sulcus (sulcus of Syl-vius) (AC13): the opercular part (A14), the triangular part (A15), and the orbital part (A16).

The parietal lobe adjoins the frontal lobe with the postcentral gyrus (A5) which is de-fined caudally by the postcentral sulcus (A17). This is followed by the superiorparietal lobule (A18) and the inferior parietal lobule (A19), which are separated by the in-traparietal sulcus (A20). The end of thelateral sulcus is surrounded by the supra-marginal gyrus (A21); theangular gyrus (A22) lies ventrally to it. The medial surface of the parietal lobe is formed by the pre-cuneus (B23).

The temporal lobe includes the temporalpole (AC24) and three major convolutions:the superior temporal gyrus (A25), the middle temporal gyrus (A26), and the inferior temporal gyrus (AC27), which are separatedby the superior temporal sulcus (A28) and the inferior temporal sulcus (A29). The trans-verse temporal gyri (Heschl ’s convolutions)of the dorsal aspect of the temporal lobe lie in the depth of the lateral sulcus. On the medial surface is the parahippocam-pal gyrus (BC30) which merges rostrally intothe uncus (BC31) and caudally into the lin-gual gyrus (BC32). It is separated by the col-lateral sulcus (BC33) from the middle occipi-totemporal gyrus (BC34). Ventrally lies the lateral occipitotemporal gyrus (BC35),delimited by the occipitotemporal sulcus (BC36).

The occipital lobe includes the occipitalpole (A–C37) and is crossed by the trans-verse occipital sulcus (A38) and the deepcal-carine sulcus (B39). Together with theparieto-occipital sulcus (B40), the latter de-fines the cuneus (B41).

The cingulate gyrus (limbic gyrus) (green) (B42) extends around the corpus callosum (B43). Caudally, it is separated by the hippo-campal sulcus (B44) from the dentate gyrus (dentate band) (B45) and tapers rostrally into the paraterminal gyrus (B46) and into the subcallosal area (parolfactory area) (B47). Isthmus of cingulate gyrus (B48).

Base of the brain.The basal aspect of thefrontal lobe is covered by the orbital gyri (C49). Along the edge of the hemisphere runs the gyrus rectus (C50), laterally defined by the olfactory sulcus (C51) into which the olfactory bulb (C52) and the olfactory tract are embedded. The olfactory tract splits into the two olfactory striae which embrace the anterior perforated substance (olfactoryarea) (C53).

C54 Hippocampal sulcus.

C55 Longitudinal cerebral fissure.