THE BASE OF THE FORE-BRAIN. 73 



parietal lobe; it fuses with the temporal lobe and the gyrus hippo- 

 campi of the limbic lobe, inferiorly. 



The olfactory lobe and the limbic lobe, comprising the rhinen- 

 cephalon and a part of the neopallium, also belong to the cerebral 

 hemisphere; but no part of either can be seen on the convex sur- 

 face (Figs. 28, 21 and 18). 



THE BASE OF THE FORE-BRAIN. 



The basal or inferior surface of the fore-brain comprises the 

 inferior surface, first, of the end-brain, including the pars optica 

 hypothalami and the cerebral hemispheres; and, second, of the 

 inter-brain, which embraces the pars mammillaris hypothalami. 

 It is completely exposed only when a section is made through the 

 mid-brain and the rhombencephalon removed (Figs. 21 and 26). 

 This should now be done with a thin, moistened brain-knife. 

 Make the section from before backward and upward, at a right 

 angle to the axis of the mid-brain. Now notice, first, the section 

 of the mid-brain and, just anterior to that, the median structures 

 of the fore-brain, occupying the center of the field; and, second, 

 the surrounding inferior surface of the cerebral hemispheres. 

 The latter form the very large peripheral zone. 



The base of the cerebral hemisphere extends from the frontal 

 to the occipital pole. In front it is composed of the orbital area 

 bounded by the medial orbital and superciliary borders ; and, pos- 

 teriorly, is made up of the tentorial area, which is bounded, later- 

 ally, by the infero-lateral border, and, medially, by the chorioidal 

 fissure and the medial occipital margin of the hemisphere (Fig. 

 26). The orbital area embraces the inferior surface of the frontal 

 lobe and of the island, and the whole olfactory lobe; while the 

 inferior surface of the temporal and occipital lobes, and the gyrus 

 hippocampi and fascia dentata of the limbic lobe are included in 

 the tentorial area. 



Frontal Lobe, Inferior Surface (Fig. 26). The inferior surface 

 of the frontal lobe, resting on the orbital plate of the frontal bone, 

 is often called the orbital lobe. It is separated from its fellow 

 by the longitudinal fissure of the cerebrum, and is bounded behind 



