204 



HEAD AND NECK 



head forwards. Support it in this position, and make two incisions through 

 the dura mater in an antero-posterior direction one on each side of the 

 superior sagittal sinus, and along its whole length. From the mid- 

 point of each of these incisions another cut must be made through each 

 lateral portion of the dura mater downwards to the cut margin of the skull 

 immediately above the ear (Fig. 85). The dura mater covering the upper 

 aspect of the brain is thus divided into a central strip containing the 

 superior sagittal sinus, and four triangular flaps. The flaps should 

 now be turned downwards over the cut margin of the skull, and in this 

 position they preserve the brain, during its removal, from laceration by the 

 sharp bony edge. 



Lateral lacuna 



Arachnoideal 

 granulation 



Sagittal 



Blood vessels 



Grey cortex 



of a gyrus 



Arachnoideal granulation 

 Lateral lacuna 



Dura mater 



Pia mater 

 Subarachnoid space 



Arachnoid 



Falx cerebri 



FIG. 84. Diagram of a frontal section through the middle portion of the 

 cranial vault and subjacent brain to show the membranes of the brain 

 and the arachnoideal granulations. 



Cavum Subdurale. The subdural space is the term applied 

 to the interval between the dura mater and the arachnoid 

 Figs. 83 and 84. It contains a very small quantity of serous 

 fluid, which moistens the opposed surfaces of the membranes. 

 A striking contrast between the two surfaces of the dura 

 mater will be noted. The external surface is rough and 

 flocculent ; the internal surface is smooth and glistening. 



Venae Cerebri. The cerebral veins which return the blood 

 from the surface of the cerebral hemispheres will be seen 

 shining through the arachnoid. They are lodged for the 

 most part in the sulci between the gyri, and run upwards 

 to the median plane. When they reach the superior sagittal 

 sinus they turn anteriorly, and lie against the wall of the sinus, 

 for some distance, before they open into it. 



