4 6 



The Encephahn 



In operating, the trephine must not be applied at a lower level, lest 

 the lateral sinus be opened (p. 39). 



The fissure of Sylvius runs backwards and upwards between the 

 frontal and the temporo-sphenoidal lobes. As the frontal lobe rests 

 upon the roof of the orbit, the fissure must start from just below the 

 level of the roof; it begins about \\ in. behind the external angular 

 process of the frontal bone, and runs to the parietal eminence not 

 quite to its centre, for that is occupied by the supra-marginal gyms, 

 which takes its name from being ' above the end ' of the fissure. 

 The main fissure runs for about \ in. before it divides into its vertical 

 and horizontal limbs ; the former ascends for about i in., and the 

 latter runs backwards and upwards through about the middle of the 

 hemisphere. 



The paricto-occipital fissure begins in the interior of the longi- 



Outer Surface of Left Hemisphere. (GRAY.) 



