B

The floor of the third ventricle is formed (from anterior to posterior) by the optic chiasm/optic stalk region, the tuber cinereum with the infundibulum (pituitary stalk), and the paired mammillary bodies; the oculomotor (third) nerve runs lateral and caudal to the ventricle and is not a component of its floor [Baka 1993 PMID 8357622; Buelens 2011 PMID 21240510].