A, The olfactory tract extends along the olfactory sulcus on the lateral side of the gyrus rectus and divides at the edge of the anterior perforated substance into the medial and lateral olfactory striae. The orbital surface lateral to the gyrus rectus is divided by an H-shaped sulcus into anterior, posterior, medial, and lateral orbital gyri. B, Another cerebrum. The olfactory sulci separate the gyrus rectus medially from the orbital gyri laterally. The orbital surface lateral to the gyrus rectus is divided by a number of sulci that tend to form an H-shaped configuration and divide the area into anterior, posterior, medial, and lateral orbital gyri. The most lateral of the lateral orbital gyri is continuous with the pars orbitalis of the inferior frontal gyrus. C, Orbital surfaces of another hemisphere. The location of the frontal and temporal horns deep within the hemisphere has been outlined using colored black pins. The frontal horn extends forward in the frontal lobe to approximately the level of the transverse part of the H-shaped orbital sulcus. The deep site of the foramen of Monro, shown with yellow pins, in relationship to the basal surface is anterior to the mamillary bodies. D, The lower part of the right frontal lobe has been removed to expose the frontal horn. The caudate nucleus forms the lateral wall of the frontal horn and the rostrum of the corpus callosum forms the floor. At a more superior axial level, the caudate and lentiform nuclei are separated by the anterior limb of the internal capsule, but at this level below the anterior limb of the internal capsule, the nuclei form a solid, unbroken mass of gray matter located above the anterior perforated substance and adjoining part of the orbital surface. In addition, the lentiform and caudate nuclei blend medially without a clear border into the nucleus basalis and nucleus accumbens. The nucleus basalis is located in the medial part of this gray mass below the anterior commissure, and the nucleus accumbens is situated in front of the nucleus basalis. The amygdala is located below and blends into the lentiform nucleus at its upper border. E, Fiber dissection of the right hemisphere showing the relationship of the genu and rostrum of the corpus callosum to the orbital surface. The anterior margin of the genu of the corpus callosum is located above the midportion of the basal surface. The rostrum of the corpus callosum forms the floor of the frontal horn. The genu, along with its large fiber bundle, the forceps minor, forms the anterior wall of the frontal horn. The caudate nucleus forms the lateral wall of the frontal horn. The basal side of the caudate nucleus and the lentiform nucleus, formed by the putamen and globus pallidus, blend together in the area below the anterior limb of the frontal capsule to form a globular mass of gray matter that extends almost unbroken from the lower part of the frontal horn to the insula. At a more superior level, the anterior limb of the internal capsule cuts into the interval between the caudate and lentiform nuclei dividing them into separate nuclei. (Images courtesy of AL Rhoton, Jr.)