OPERATIVE TECHNIQUE 443 



flap (Fig. 292) and bleeding from the cut surface of the dura is controlled 

 with silver clips. As the mesial margin of the flap extends almost to the 

 superior sagittal sinus, there are numerous bleeding vessels which will 

 require ligature ; some of the smaller ones may be dealt with by silver 

 clips. The lateral ventricle is then tapped at the junction of its body 

 and descending horn, the cerebrospinal fluid being allowed to flow away 

 over the brain ; the needle is left in situ for as long as possible to ensure 

 complete evacuation of the ventricle. 



The next step is to divide any cerebral veins which may be running 



Fig. 292. — The Method in which the Osteoplastic Flap is raised and turned 

 outwards : Flap of Dura Mater is then turned outwards and the 

 Lateral Ventricle tapped. 



from the upper part of the hemisphere into the superior sagittal sinus. 

 There are five or six of these veins, and they can be secured between fine 

 ligatures or silver clips. Care should be taken to avoid injury to the vein 

 which drains the Rolandic area of the brain, otherwise a transient hemi- 

 plegia may result. 



After the cerebral veins have been divided the whole of the posterior 

 extremity of the hemisphere is to be retracted to such an extent as to 

 expose the falx cerebri (Fig. 293). Continued retraction will bring the 

 inferior longitudinal sinus into view, and beneath it the corpus callosum 

 (Fig. 294). To obtain an adequate exposure of the splenium of the 

 corpus callosum, it is often advisable to divide the inferior longitudinal 



