TI-weighted, Optic Chiasm. This section is at the level between the superior and inferior colliculi. in the tectum of the midbrain. The intra-axial (intra-brain-stem) fibers of the oculomotor nerve course from their origin in the oculo motor nucleus through the mesencephalic tegmentum through RN and CPo ACi is seen in its circummesence phalic location anterior to and continuous with the quadri geminal plate cistern. MaB is a prominent structure between PS and the midbrain. ACi = Ambient Cistern, CP = Cerebral Peduncle, HG = Hippocampal Gyrus, ICi = Interpeduncular Cistern, MaB = Mamillary Body, OC = Optic Chiasm, ON = Optic Nerve, OT = Optic Tract, PS = Pituitary Stalk, RN = Red Nucleus, SN = Substantia Nigra, U = Uncus of Temporal Lobe.