396 THE BRAIN 



not probable that the dissector will find any trace of them on 

 the brain. 



THE CEREBRUM. 



The term cerebrum includes (i) the two cerebral hemi- 

 spheres which, together, form the telencephalon and (2) the 

 boundaries of the third ventricle which, collectively, form the 

 diencephalon. The two parts, that is the telencephalon and 

 the diencephalon, are intimately connected with one another. 



Each hemisphere is separated from its fellow of the oppo- 

 site side by a deep fissure called the longitudinal fissure. 

 Anteriorly and posteriorly the longitudinal fissure completely 

 separates the two hemispheres, but in the intermediate 

 region the hemispheres are connected with one another, 

 across the bottom of the longitudinal fissure by a large trans- 

 verse commissure called the corpus callosum, which can be 

 seen when the hemispheres are drawn apart. 



Cerebral Hemispheres. It has been pointed out already 

 that each cerebral hemisphere possesses three surfaces, three 

 poles and five borders. The surfaces are supero- lateral, 

 medial and inferior. The poles are frontal, occipital and 

 temporal. The borders are supero -medial, infero- lateral, 

 superciliary, medial orbital and medial occipital. 



The frontal pole is the most projecting part of the anterior 

 extremity of the hemisphere. It is blunt and rounded, and 

 it lies behind the medial part of the superciliary eminence 

 of the frontal bone. The occipital pole is the posterior ex- 

 tremity of the hemisphere. It is more pointed than the 

 frontal pole. It lies immediately above and lateral to the 

 external occipital protuberance (inion). In a well-hardened 

 brain the occipital pole of the right hemisphere is usually 

 marked, on its medial aspect, by a broad groove caused by 

 the posterior end of the superior sagittal sinus. 



The supero-lateral surface is convex and is adapted to the 

 concavity of the cranial vault. The medial surface is flat 

 and, when the brain is in situ, it is more or less completely 

 separated from the corresponding surface of the opposite 

 hemisphere by the falx cerebri and the prolongations of the 

 arachnoid and the pia mater which occupy the longitudinal 

 fissure between the two hemispheres. The inferior surface is 

 irregular and is adapted to the floors of the anterior and 



