The fornix commissure is a triangular and slender sheet of transverse fibers. It is located inside of the brain's fornix. It is commonly known either as commissure of fornix or hippocampal commissure. The commissure attaches the posterior pillars' medial edges within the fornix. The fornix of brain is a cluster of axons that is responsible for transmitting signals between the mamillary bodies, the septal nuclei, and the hippocampus. The back sections of the fornix are connected together by the psalterium, which are thin lamina. The psalterium, which is also known by the name lyra, consists of transverse fibers that bring together a pair of hippocampi along the center. All together, these make up the commissure of fornix. The terminal and ending lamina forms the plate of the commissure. This makes way for the septum pellucidum, the corpus callosum, and the fornix. The fornix commissure is situated near the uncus, the anterior pillars of fornix, the fimbria, and the crus fornicis.