The orbital surface presents five gyri:
- the gyrus rectus
- the anterior, posterior, medial, and lateral orbital gyri
- the frontomarginal gyrus (located between the orbital and the lateral surfaces)
The orbital surface is crossed by two main sulci:
- the olfactory sulcus
- the H-shaped orbital sulcus
Sometimes, the typical subdivision into four orbital gyri is not well defined.
The gyrus extending on the edge between the medial and inferior surfaces of the frontal lobe. It is medial to the olfactory sulcus, and inferior to the supraorbital sulcus.
It is bounded posteriorly by the anterior perforated substance and the subcallosal gyrus. On the medial surface, the medial limit is represented by the interhemispheric fissure.
The deep fissure located on the medial-basal surface of the frontal lobe containing the olfactory bulb and its tract. It separates the lateral surface of the gyrus rectus from the medial surface of the orbital gyri.
The H shaped sulcus formed by a transverse sulcus in the middle and two lateral sagittal sulci. it separates the 4 orbital gyri. The longitudinal sulci are called medial and lateral orbital sulci; they cross the transverse orbital sulcus. This characteristic form, however, presents a great variability.
The medial orbital sulcus is divided into rostral and caudal segments: the rostral portion separates the anterior orbital gyrus from the medial orbital gyrus; the caudal portion divides the medial orbital gyrus from the posterior one.
The lateral orbital sulcus is also divided into two segments: the rostral portion separates the anterior orbital gyrus from the lateral one; the caudal portion divides the posterior orbital gyrus from the lateral one. The transverse orbital sulcus crosses the longitudinal sulci in their middle point, separating the anterior from the posterior orbital gyri.
Anterior orbital gyrus
The gyrus located on the anterior part of the frontal lobe, between the medial and lateral orbital gyri and anterior to the transverse orbital sulcus. Sometimes, accessory sulci split this gyrus.
Posterior orbital gyrus
The gyrus located between the medial and lateral orbital gyri. It is bounded posteriorly by the anterior perforated substance and anteriorly by the transverse orbital sulcus. Sometimes, accessory sulci split this gyrus.
Medial orbital gyrus
The gyrus included between the gyrus rectus medially and the anterior and posterior orbital gyri laterally. Sometimes, accessory sulci split this gyrus.
Lateral orbital gyrus
The gyrus placed between the lateral orbital sulcus and the inferolateral margin of the hemisphere.
The inferior surface of the lobe is marked, from medial to lateral, by three horizontal sulci:
- the rhinal sulcus
- the collateral sulcus
- the occipital temporal sulcus.
They bound, from medial to lateral:
- the parahippocampal gyrus
- the occipital temporal gyrus
- the inferior temporal gyrus
The longest sulcus on the inferior surface of the temporal lobe, running horizontally from the anterior region of the temporal lobe to the occipital lobe. Anteriorly, it separates the parahippocampal gyrus from the lateral occipito-temporal gyrus; posteriorly it divides the lateral occipito-temporal gyrus from the lingula.
It is formed, from anterior to posterior, by three different portions: the rhinal sulcus /orange/, the collateral sulcus proper /green/, and the caudal (occipital) collateral sulcus /blue/.
The segment of the collateral sulcus containing the common temporal artery, which originates from the posterior cerebral artery. When this sulcus is present, it divides the parahippocampal gyrus into the anterior and posterior parts.
The sulcus running parallel to the collateral sulcus that divides the lateral portion of the lateral occipito-temporal gyrus from the basal surface of the inferior temporal gyrus.
The anterior, short, longitudinal segment of the collateral sulcus that separates the uncus from the anterior portion of the fusiform gyrus.
The convolution on the medial surface of the temporal lobe which is part of the limbic lobe. it is limited by the basal surface of the superior temporal gyrus anteriorly, by the uncus medially, the fusiform gyrus laterally and by the lingula posteriorly.
Its antero-posterior extension corresponds to the level of the rostrum and the splenium of the corpus callosum.
It /green/ participates to form the medial occipitotemporal gyrus /blue/ together with the lingual gyrus. It is formed by four portions: the piriform area, the presubiculum, the entorhinal area, and the posterior parahippocampal gyrus. The uncus /orange/ is medially.
Lateral occipito-temporal gyrus
The gyrus extending from the inferior surface of the temporal lobe to the occipital lobe, also known as fusiform gyrus. It can also be divided into anterior fusiform gyrus and posterior fusiform gyrus.
On the anterior surface, it is bounded by the temporal pole; on the medial surface the collateral sulcus divides it from the parahippocampal and lingual gyri.
Its /orange/ lateral border is represented by the occipito-temporal sulcus, which separates it from the inferior temporal gyrus /green/. The posterior border is the occipital pole.
The basal surface is continuous to the basal surface of the temporal lobe. It presents the prolongation of gyri and sulci that can be seen on the inferior surface of the temporal lobe.
Anterior perforated substance
The portion of gray matter crossed by venous and arterial components: perforating arteries from the internal carotid, anterior and middle cerebral arteries, and inferior striate veins.
On the anterior surface, it is limited by the olfactory striae and on the medial surface by the optic chiasm. Laterally, it is bordered by the limen insulae and the temporal lobe.
The most anterior part of the floor of the third ventricle. It is part of the optic pathways. Neurons transmitting information from the nasal part of the retina cross to the contralateral optic tract at this level.
The part of the optic pathway visible on the inferior surface of the brain extending between the optic chiasm to the lateral geniculate body. It transmits the information from the contralateral half of the visual field.
The inferior extension of the tuber cinereum connecting the hypothalamus to the pituitary gland, also called pituitary stalk. It pierces the diaphragm sellae at the level of the skull base.
The endocrine gland constituting the connection between the central nervous system and the peripheral endocrine organs. It is located inside the sella turcica of the sphenoid bone, hanging from the inferior surface of the brain thanks to the pituitary stalk.
The anterior portion of the interpenduncular region, limited by the optic chiasm, anteriorly, and the two mammillary bodies, posteriorly.
It constitutes part of the floor of the third ventricle and hosts the infundibulum of the pituitary gland, which subdivides the tuber into H shape: the anterior, posterior, right and left areas.
The inferior ends of the anterior portion of the fornix constituting the posterior portion of the floor of the third ventricle, being located behind the tuber cinereum.