The under surface of the cerebrum shows some important features, which, passing from before backward, are as follows: ( 1 ) the longitudinal fissure, separating the frontal lobes. (3) The corpus eallosuln, appearing in the depth of the longitudinal fissure and serving as, a great transverse commissure connecting the two hemi spheres. (3) The olfactory nerve with its ex panded extremity the olfactory bulb, lying in 31 groove in the under surface of the frontal lobe. (41 The fissure of Sylvius.separating the :interior the Inidine lobe. (5) The anterior perforated spaec—so called from the perforation: for the passage of blood-vessels—is the under surface of the corpus striatum (see below). ((i) The pituitary body or hypophysis eerebri. (7) The infundibulum is a narrow tube of gray matter connecting the pituitary body with (g) the (tuber eineremn. an eminence of gray matter lying 1.0 WCCII the diverging cerebral peduncles. 0) The corpora albicantia or corpora mamillaria are two small white protuberances each about the size of a pea just behind the tuber cinereum. They arc composed externally of white matter, internally of gray matter, and are formed by the anterior crura of the fornix. (10) The pos
terior perforated space lies between the corpora albicantia and the anterior fibres of the pons. Its perforations are due to vessels which pass to the optic thalami. (11 ) The optic commissure is the crossing of the right and the left optic tracts to form the optic nerves. It is situated just in front of the tuber cinerenni. (See also below—optic nerve, under (rallied .V (TUC'S.) (12) The cerebral peduncles or crura cerebri are two diverging bundles of white fibres which appear to come out from behind the anterior border of the pons. Each peduncle passes upward, for ward, and outward, and enters the under surface of the hemisphere. (For description of cerebral peduncles, see above under Mid-Brain.) (13) The under surface of the cerebrum also shows the exit of the third and fourth cranial nerves, the former coming out from the inner margins of the (Tura in front of the polls, the latter from the outer margins in front of the polls.