Midsagittal section of the brain

Telencephalon

The telencephalon corresponds to the cerebral hemispheres and includes the cerebral cortex and several subcortical structures. The cerebral cortex is composed of gyri and sulci and divided into six lobes including the frontal, temporal, parietal, occipital, insular and limbic lobes. The divisions between lobes are primarily identified by fissures. The midsagittal aspect of the cerebrum also reveals structures spanning the longitudinal cerebral fissure, such as the corpus callosum. The corpus callosum is a prominent structure on this midsagittal surface composed of commissural fibers that permit the direct communication between the structures of the two hemispheres. The septum pellucidum is a thin membrane connected to the inferior surface of the corpus callosum and located at the midline of the brain.

The most prominent of the sulci is the cingulate sulcus (sulcus cinguli), which follows a curved course parallel to the upper convex margin of the corpus callosum. Anteriorly, the sulcus cinguli ends below the rostrum of the corpus callosum, and posteriorly, it turns upwards to reach the superomedial border, a little behind the upper end of the central sulcus (this posterosuperior extension of the cingulate sulcus is called marginal sulcus). The area between the cingulate sulcus and the corpus callosum is the gyrus cinguli (or cingulate gyrus), which is a part of the so called limbic lobe. Hence this gyrus is defined by the cingulate sulcus superiorly, and the corpus callosum inferiorly (specifically by the callosal sulcus which wounds around the corpus callosum).

Above the cingulate sulcus, up to the limit of the superomedial border (or edge) is an area which consists of two parts. The large anterior part, called the medial frontal gyrus, lies anterior to the paracentral lobule, which is wound around the end of the central sulcus. The anterior border of the paracentral lobule is the paracentral sulcus, which separates this lobule from the medial frontal gyrus. The paracentral sulcus is a very short sulcus which is continuous with the cingulate sulcus. The medial frontal gyrus and anterior part of the paracentral lobule are part of the frontal lobe. 

Between the parietooccipital sulcus and paracentral lobule is a quadrilateral area called the precuneus. Anteroinferiorly, the precuneus is separated from the posterior part of the gyrus cinguli by the suprasplenial (or subparietal) sulcus. The precuneus and the posterior part of the paracentral lobule form the medial surface of the parietal lobe.

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Further posterior to the paracentral lobule and gyrus cinguli are two major sulci that cut off a triangular area. This area is called the cuneus, which is a part of the occipital lobe. This triangular area is defined anterosuperiorly by the parieto-occipital sulcus (which crosses the superomedial border to appear as a very short sulcus on the superolateral surface), inferiorly by the calcarine sulcus, and posteriorly by the superomedial border of the cerebral cortex. The calcarine sulcus extends forward beyond its junction with the parietooccipital sulcus and ends a little below the splenium of the corpus callosum (posterior part of the corpus callosum) to define a small area called the isthmus which lies between it (calcarine sulcus) and the splenium of the corpus callosum.

The brain can be divided into Brodmann areas according to its cytoarchitecture and function. The medial frontal gyrus contains Brodmann area 6 (premotor and supplementary motor cortex) and area 8 (part of the motor association cortex). The paracentral lobule surrounds the medial end of the central sulcus and, because of that, it contains the Broadman area 4 (the primary motor cortex), areas 3, 1, and 2 (the primary somatosensory cortex) and area 5 (the somatosensory association cortex). The cuneus contains Brodmann areas associated with the process of visual information (areas 17, 18 and 19). These areas are not exclusively seen in the medial view of the brain and extend into the lateral aspect of the cerebral hemispheres.

Diencephalon

The diencephalon is a phylogenetically older part of the brain lying between the telencephalon and the brainstem. It is composed of the thalamus, the hypothalamus, the subthalamus and the epithalamus.

The thalamus is a large mass of grey matter with symmetrical halves located on each side of the third ventricle. The thalamus has several functions that include relaying of sensory and motor information to the cerebral cortex. The interthalamic adhesion expands between the two halves of the thalamus. 

The hypothalamus is the part of the diencephalon that lies below the thalamus. It comprises several subdivisions and nuclei that are responsible for controlling important physiological functions such as hormone regulation. It works closely with the pituitary gland to perform this function. Just anterior inferior to the hypothalamus is the optic chiasm, where nerves from each eye cross over allowing binocular vision.

The main component of the epithalamus is the pineal gland or epiphysis, which produces a hormone called melatonin that regulates circadian rhythms.

The subthalamus lies inferior to the posterior part of the thalamus, just posterior and lateral to the hypothalamus. The largest division of the subthalamus is the subthalamic nucleus. This nucleus plays a fundamental role in the circuitry of the basal ganglia (i.e. movement regulation).