460 THE BRAIN 



from the lateral surface. The infero-lateral border marks off 

 the tentorial part of the inferior surface from the lateral 

 surface. The medial occipital border is not very distinct, 

 except in cases where the brain has been hardened in situ. 

 It extends from the posterior extremity of the hemisphere to 

 the posterior end of the corpus callosum, and intervenes 

 between the medial surface and the tentorial part of the inferior 

 surface. The medial orbital margin extends from the frontal 

 pole to the lamina terminalis and separates the orbital from 

 the medial surface. 



The most projecting part of the anterior end of the 

 cerebral hemisphere is called the frontal pole, whilst the 

 most projecting part of the posterior end is termed the 

 occipital pole. On the under surface of the hemisphere, the 

 prominent rounded portion of cerebral substance which ex- 

 tends anteriorly below the lateral fissure receives the name of 

 the temporal pole. In a well-hardened brain a broad groove is 

 usually present on the medial aspect of the occipital pole of 

 the right hemisphere. This corresponds to the termination 

 superior sagittal venous sinus. 



Longitudinal Fissure. This great median cleft is occupied 

 by the fold of dura mater termed the falx cerebri. Anteriorly 

 and posteriorly, it completely separates the cerebral hemi- 

 spheres from each other, but the intermediate part is floored 

 by the corpus callosum the commissural band which passes 

 between the hemispheres and connects them together. The 

 upper surface of the corpus callosum can be displayed by 

 gently drawing asunder the two sides of the longitudinal 

 fissure. 



Dissection. If two brains are available, the dissector is advised, at this 

 stage, to separate the cerebrum from the cerebellum, pons and medulla 

 oblongata in one of them, by cutting transversely through the mid brain if 

 this has not been done already. The cerebrum may then be split in the 

 median plane by placing a long knife in the longitudinal fissure and divid- 

 ing, with one sweep, the various parts which connect the two sides to each 

 other. By this proceeding, the three surfaces of each cerebral hemisphere 

 are exposed, and the gyri and sulci can be studied fully and satisfactorily. 

 If only one brain is at the disposal of the student, he should not, at this stage, 

 separate the cerebral hemispheres from each other, but should endeavour 

 to follow out the gyri and sulci with the various parts of the brain in 

 position. No doubt he studies the hemisphere in this way at a dis- 

 advantage, but as the dissection proceeds, opportunities will occur which 

 will enable him to examine those districts of the surface which he can see 

 only imperfectly at present. 



Cerebral Gyri and Sulci. The surfaces of the cerebral 



