The<unk>  median fissure (ventral or ventromedian fissure) contains a fold of pia mater, and extends along the entire length of the<unk><unk> : It ends at the lower border of the pons in a small triangular expansion, termed the foramen cecum. Its lower part is interrupted by bundles of fibers that cross obliquely from one side to the other, and constitute the pyramidal decussation. Some fibers, termed the<unk>  external arcuate fibers, emerge from the fissure above this decussation and curve lateralward and upward over the surface of the<unk><unk>  to join the inferior peduncle.
Anterior median fissure of the medulla oblongata
Posterolateral sulcus of medulla oblongata
Anterior median fissure of spinal cord
Horizontal fissure of cerebellum
Medial eminence of floor of fourth ventricle
Paramedian pontine reticular formation
Middle cerebellar peduncle
Fourth ventricle