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The fornix continues in an arc to the anterior commissure. The hippocampal commissure provides one of two major paths whereby the hippocampi communicate with each other.Īfter the hippocampal commissure the single fiber bundle is properly referred to as the fornix. The two crua come together and form the hippocampal commissure. The fimbria of each hippocampus thickens as it moves posteriorly and eventually splits off from the hippocampus forming the crua or “legs” (singular-crus) of each hippocampus. The fimbria looks like a thick rubber band. Fimbria means fringe and in this case it is the fringe of the hippocampus. As the fibers of the alveus travel posteriorly, they aggregate medially to form the fimbria of the fornix. The alveus is white matter consisting of myelinated afferents and efferents. The fornix begins as the bundle of fibers called the alveus. The fornix is a “C” shaped tract (in sagittal section). Structure of the hippocampus, uncus, crua, fornix, anterior commissure, precommissural fornix, postcommissural fornix, and columns. Each hippocampus looks like a seahorse due to the way it is folded during development. A hippocampal formation is located in the temporal lobe of each cerebral cortex, medial to the inferior horn of the lateral ventricle.
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The term hippocampal formation typically refers to the dentate gyrus, the hippocampus proper (i.e., cornu ammonis), and the subicular cortex. (Some experts would also include parts of the hypothalamus, thalamus, midbrain reticular formation, and olfactory areas in the limbic system.) These last three cortical areas comprise different portions of the temporal lobe. The limbic system includes the hippocampal formation, amygdala, septal nuclei, cingulate cortex, entorhinal cortex, perirhinal cortex, and parahippocampal cortex. In this case, the border is between the neocortex and the subcortical structures (diencephalon). Like the familiar word “limbo”, it means an intermediate or transitional state, which is a border. Limbic is a Latin term which means border.