360 THE BRAIN 



sulcus and the anterior and posterior central gyri. He will 

 note also that, immediately below the lower end of the central 

 sulcus, more rarely continuous with it, there is a very well- 

 marked antero-posterior cleft ; it is the posterior ramus of the 

 lateral fissure (Sylvian) (Fig. 135). The lateral fissure com- 

 mences on the inferior surface of the hemisphere (Fig. 138), 

 and divides, immediately after it reaches the lateral surface, 

 into anterior horizontal, anterior ascending, and posterior rami, 

 all of which the dissector must identify (Figs. 135, 152). The 

 posterior ramus is always easily identified, but the anterior 

 rami may present difficulty. 



The part of the hemisphere which lies below the lateral 

 fissure is the anterior part of the temporal lobe; it ends 

 anteriorly in a rounded point called the temporal pole. 



The dissector should next turn his attention to the borders 

 of the hemisphere as seen from the lateral side (Fig. 135). 

 They are supero-medial, infero-lateral, and superciliary. 



The supero-medial border is convex. It extends from the 

 frontal pole to the occipital pole, along the side of the 

 superior sagittal venous sinus, and separates the supero-lateral 

 surface from the medial surface. 



The infero-lateral border is concavo-convex. It extends 

 from the occipital to the temporal pole. Its posterior and 

 larger part lies along the line of the transverse venous sinus, 

 and its anterior part runs along the line of the petro-squamous 

 suture. It separates the supero-lateral surface from the 

 posterior part of the inferior surface of the hemisphere. On 

 this border, about a third of its length from the occipital 

 pole, there is a distinct notch, called the pre-occipital notch, 

 caused by the terminal portion of a vein which descends on 

 the hemisphere to the transverse sinus. 



The superciliary border extends from the temporal pole to 

 the frontal pole. It corresponds in position, anteriorly, with 

 the superciliary arch of the skull, and it separates the supero- 

 lateral surface from the anterior or orbital part of the inferior 

 surface. The dissector should verify the above statements by 

 placing his specimen, if possible, in sagittal and horizontal 

 sections of skulls of convenient size. 



For purposes of description and localisation the greater 

 part of each hemisphere is divided, by means of fissures and 

 sulci, into areas called lobes, and within the area of each lobe 

 there are, as a rule, several gyri. 



