THE CEREBRUM 397 



middle cranial fossae, and to the upper surface of the ten- 

 torium cerebelli. It is separated into anterior and posterior 

 parts by a deep transverse fissure called the stem of the 

 lateral fissure. The anterior or orbital part lies on the floor 

 of the anterior fossa, that is on the roof of the orbit. It is 

 concave, and it looks downwards and laterally ; consequently 

 it is partially visible when the hemisphere is viewed from the 

 lateral side (see Figs. 152, 155). The posterior part is 

 concavo-convex. It looks downwards and medially. Its 

 anterior extremity forms the rounded temporal pole, which 

 abuts against the posterior part of the lateral wall of the 

 orbit. Behind the temporal pole its anterior convex part 

 lies on the anterior part of the floor of the middle cranial 

 fossa which separates it from the infra-temporal fossa. The 

 anterior part of its concave portion rests upon the anterior 

 surface of the petrous part of the temporal bone which 

 separates it from the tympanic cavity, the internal ear and 

 the carotid canal. It is separated from the anterior surface 

 of the apex of the petrous part of the temporal bone by the 

 semilunar ganglion of the trigeminal nerve, and it is marked 

 near its lateral margin by a depression caused by the eminentia 

 arcuata of the temporal bone. 



The posterior and longer part of the concave area rests 

 upon the tentorium cerebelli which intervenes between it and 

 the cerebellum. 



The supero-medial border extends from the frontal to the 

 occipital pole ; it is convex and is in relation with the wall of 

 the superior sagittal sinus. 



The infero-lateral border is concave in the posterior part 

 of its extent, where it rests upon the tentorium cerebelli and 

 is in relation with the wall of the transverse sinus ; and the 

 anterior part, which lies along the line of union of the 

 squamous with the petrous part of the temporal bone, is 

 convex. 



The superciliary border extends from the frontal to the 

 temporal pole. It lies parallel with and above the supra- 

 orbital margin. It separates the supero-lateral surface from 

 the orbital part of the inferior surface. 



The medial orbital margin can be seen at the base of the 

 brain ; it extends from the frontal pole to the optic chiasma, 

 along the side of the inferior part of the anterior portion of 

 the longitudinal fissure. It lies above the roof of the nose. 



