GENERAL FEATURES 363 



orbital border, which runs from a point immediately in front 

 of the optic chiasma to the frontal pole, separating the medial 

 surface from the anterior part of the inferior surface. 



Between the medial occipital and the medial orbital 

 borders the lower boundary of the medial surface is formed 

 by the lower margin of the splenium and the lower margin of 

 the fornix, which lie immediately above the diencephalon. 



The corpus caliosum is separated from the gyrus cinguli, 

 which is immediately adjacent to it, by the callosal sulcus 

 (Fig. 136). 



The gyrus cinguli is separated from the adjacent parts of 

 the medial surfaces of the frontal and parietal lobes by the 

 sulcus cinguli, which turns upwards at its posterior end, and 

 cuts the supero-medial border of the hemisphere, a short 

 distance behind the upper end of the central sulcus (Figs. 

 136, 156). 



Some distance in front of its posterior end, the sulcus 

 cinguli gives off a branch which ascends towards the supero- 

 medial border. That branch is not named but it lies parallel 

 with, or slightly in front of, the pre-central sulcus on the 

 supero-lateral surface of the hemisphere. The portion of 

 the medial surface of the hemisphere which lies between the 

 posterior end of the sulcus cinguli and the unnamed upturned 

 branch, corresponds in a general way with the upper ends 

 of the posterior and anterior central gyri, and it is termed the 

 paracentral lobule (Figs. 136, 159). 



The part of the medial surface above the sulcus cinguli 

 and between the frontal pole and the paracentral lobule 

 is the medial part of the superior frontal gyrus ; and the part 

 which extends from the frontal pole to the optic chiasma, 

 below the sulcus cinguli, is the gyrus rectus, which will be 

 seen also on the inferior surface. 



Behind the upturned, posterior end of the sulcus cinguli, 

 but in direct line with its main portion, is a small separate 

 sulcus, called the subparietal sulcus ; and cutting the supero- 

 medial border of the hemisphere about a fourth of its length 

 from the occipital pole is the parieto-occipital fissure, which 

 crosses the posterior part of the medial surface. The lower 

 end of the parieto-occipital fissure joins an important fissure 

 called the cakarine at an acute angle. That part of the 

 medial surface which lies above the sub-parietal sulcus, and 

 between the parieto-occipital fissure and the upturned end of 



