GENERAL FEATURES 365 



corpus callosum. The wedge-shaped region of the cortex of 

 the hemisphere between the calcarine fissure and the parieto- 

 occipital fissure is called the cuneus ; and the portion of the 

 medial surface of the hemisphere below the calcarine fissure 

 is the posterior portion of the lingual gyms, the remainder of 

 which is on the inferior surface. Both the cuneus and the 

 lingual gyrus are parts of the occipital lobe. 



In the majority of cases the posterior part of the medial 

 surface of the occipital lobe is marked by a definite vertical 

 depression caused by the posterior part of the superior 

 sagittal sinus (Fig. 154). 



After the examination of the medial surface is completed, 

 the dissector should examine the lower surface of a specimen 

 from which the hind-brain and the lower part of the mid- 

 brain have been removed (Fig. 138). 



Upon each side he will note the three poles of the 

 corresponding hemisphere frontal, temporal, and occipital. 



The part anterior to the temporal pole is the anterior 

 part of the inferior surface, and at the same time it is the 

 inferior surface of the frontal lobe. 



It is bounded, anteriorly and laterally, by the superciliary 

 border; medially, by the medial orbital border; and, 

 posteriorly, in the lateral and greater part of its extent, by 

 the stem of the lateral fissure, which separates it from the 

 temporal lobe, but the medial part of its posterior boundary 

 is a sulcus which intervenes between it and a small 

 triangular area at the side of the optic chiasma, called the 

 anterior perforated substance. Lying parallel with the medial 

 orbital border is a sulcus, the olfactory sulcus, in which the 

 olfactory bulb and the .olfactory tract are lodged. The gyrus 

 which lies to the medial side of the olfactory sulcus is the 

 gyrus rectus, already seen on the medial surface of the hemi- 

 sphere. The portion of the surface which lies lateral to the 

 olfactory sulcus is concave, the concavity being due to the 

 upward projection of the roof of the orbit on which it rests, 

 and the gyri of this area are called orbital gyri. As a rule, 

 there are four orbital gyri, a medial, a lateral, an anterior, 

 and a posterior ; they are separated from one another by a 

 series of sulci, the orbital sulci, which have, collectively, an 

 H-shaped outline. 



The posterior part of the inferior surface, which lies 

 behind the temporal pole, looks downwards and medially, 



