![diencephalon hippocampus anatomy diencephalon hippocampus anatomy](https://i.natgeofe.com/n/396b3487-a08e-448f-a5c7-5b2903e10193/0000015d-60e5-d1cb-a7fd-e4fda49f0000_16x9.jpg)
The crura ( posterior pillars) of the fornix are prolonged backward from the body. The columns ( anterior pillars fornicolumns) of the fornix arch downward in front of the interventricular foramina and behind the anterior commissure, and each descends through the grey matter in the lateral wall of the third ventricle to the base of the brain, where it ends in the mammillary bodies. The latter name is used because the structure resembles a lyra (or triangular harp): The two crura are the "chassis" of the lyra, and the commissure connections are the fibers. The beginning of the splitting is called the psalterium or Lyra Davidis. These two crura are joined together through the hippocampal commissure. The fornix splits into two columns at the front (anterior pillars), and then splits into two posterior crura. This structure gives existence to the corpus callosum, the septum pellucidum, and the fornix. The terminal lamina creates the commissure plate. This lamina contains some commissural fibers that connect the two hippocampi across the middle line and constitute the commissure of fornix (also called the hippocampal commissure).
![diencephalon hippocampus anatomy diencephalon hippocampus anatomy](https://slideplayer.com/slide/10279130/35/images/15/Diencephalon+Figure+7.15+Slide+7.50.jpg)
The lateral portions of the body of the fornix are joined by a thin triangular lamina, named the psalterium ( lyra). The anterior fibers ( precommissural fornix) end at the septal nuclei of the basal forebrain and nucleus accumbens of each half of the brain.The posterior fibers (called the postcommissural fornix) of each side continue through the hypothalamus to the mammillary bodies then to the anterior nuclei of thalamus.The left and right parts separate, but there is also an anterior/posterior divergence. The body of the fornix travels anteriorly and divides again near the anterior commissure. The lower edge of the septum pellucidum (the membrane that separates the lateral ventricles) is attached to the upper face of the fornix body. The bundles of fibers come together in the midline of the brain, forming the body of the fornix. The fibers begin in the hippocampus on each side of the brain as fimbriae the separate left and right sides are each called the crus of the fornix (plural crura).