Immediately caudad of the optic chiasma lies a considerable rounded gray elevation, the =tuber cinereum= (Fig. 142, _h_). This bears on its ventral surface in the natural condition the =infundibulum= (Fig. 138, _d_) with the =hypophysis= (Fig. 138, _e_); in cases where the two latter structures have been removed (Fig. 142) the tuber cinereum (_h_) bears a small longitudinal opening (_i_) for attachment of the infundibulum. The infundibulum (Fig. 138, _d_) is a hollow extension of the floor of the third ventricle, and is attached to the middle of the ventral surface of the tuber cinereum. It bears at its ventral end the hypophysis (pituitary body) (Fig. 138, _e_), a vascular non-nervous body of unknown function. The hypophysis is lodged in the sella turcica of the sphenoid bone. At its caudal border the tuber cinereum bears two white elevations, the =mammillary bodies= (corpora mammillaria) (Fig. 142, _g_). [Illustration: FIG. 143.--LONGITUDINAL MEDIAN SECTION OF BRAIN. _I_, olfactory bulb; _II_, cerebrum; _III_, section of cerebellum, showing “arbor vitæ”; _IV_, medulla oblongata. _a_, tractus olfactorius; _b_, substantia perforata anterior; _c_, anterior commissure; _d_, lamina terminalis; _e_, optic chiasma; _f_, massa intermedia of thalamus; _g′_, infundibulum; _g_, hypophysis; _h_, third ventricle; _i_, mammillary body; _j_, aqueductus cerebri (or aqueduct of Sylvius); _k_, pons; _l_, velum medullare anterius; _m_, fourth ventricle; _n_, velum medullare posterius; _o_, continuation of canal of spinal cord; _p_, corpus callosum (body); _q_, genu of corpus callosum; _r_, rostrum; _s_, splenium; _t_, septum pellucidum; _u_, fornix; _v_, pillars of fornix; _w_, choroid plexus of third ventricle; _x_, stria medullaris; _y_, corpus pineale; _z_, cranial corpus quadrigeminum; _z′_, posterior commissure. 1, sulcus falcialis; 2, sulcus cruciatus; 3, sulcus splenialis; 4, sulcus marginalis; 5, sulcus supracallosalis (or callosalis).]