The fornix crura, or better known as the crus or crura of fornix, are flattened bands that are closely connected to the bottom part of the corpus callosum. The corpus callosum is a flat, wide bundle of neural fibers that are located underneath the cortex at the longitudinal fissure inside the eutherian brain. The crura are prolonged from the body in a backwards direction. Once the fornix crura diverge from one another, each part curves around the thalamus at the posterior end, passing forward and downward into the lateral ventricle's inferior cornu. The fornix crura then lie along the hippocampus' concavity, on the surface where some of the fibers form the alveus by spreading out. The remaining fibers continue along as a white, narrow band -- called the fimbria hippocampi -- and prolongs itself into the hippocampal gyrus' uncus. The uncus is the hippocampal gyrus' anterior extremity. The thalamus, hippocampi, corpus callosum, fimbria, uncus and lateral ventricle all extend from the fornix crura.