REMOVAL OF THE BRAIN 211 



basalts, and immediately above it, running anteriorly, is the 

 slender fourth cerebral nerve. If the free border of the 

 tentorium is turned laterally, at the point where it is crossing 

 the attached border, the fourth nerve will be seen perforating 

 the inner layer of the dura mater to enter the wall of the 

 cavernous sinus. 



When the dissectors have verified the facts noted above, 

 they should examine the lower free border of the falx cerebri, 

 in which they will find the small inferior sagittal sinus, which 

 terminates posteriorly, at the apex of the tentorium, in the 

 straight sinus. The straight sinus must now be opened by 

 carrying the knife posteriorly through the falx cerebri along 

 its line of union with the tentorium. Then the falx cerebri 

 must be cut away from the occipital bone, and as this is done 

 the posterior part of the superior sagittal sinus will be opened 

 up. After the falx has been removed the right and left 

 transverse and the right and left superior petrosal sinuses must 

 be opened by incisions carried along the attached border of 

 the tentorium (Fig. 88). The dissectors will probably find 

 that the superior sagittal sinus turns to the right and becomes 

 continuous with the right transverse sinus, whilst the posterior 

 end of the straight sinus turns to the left and joins the left 

 transverse sinus. In a certain number of cases this arrange- 

 ment is reversed, and not uncommonly, as in the specimen 

 shown in Fig. 88, there is a communication between the 

 right and left transverse sinuses across the front of the internal 

 occipital protuberance. Occasionally the superior sagittal, 

 the two transverse sinuses, the straight sinus, and the occi- 

 pital sinus unite anterior to the internal occipital protuber- 

 ance in a common dilatation, the confluens sinuum (O.T. 

 torcular Herophili). The transverse sinus, on each side, runs 

 from the internal occipital protuberance to the lateral end of 

 the superior border of the petrous part of the temporal bone, 

 where it dips downwards into the posterior fossa, and at the 

 same point it is joined by the superior petrosal sinus, which 

 runs postero-laterally along the superior border of the petrous 

 part of the temporal bone from the cavernous sinus to the 

 transverse sinus, connecting the two together. 



Dissection. With the point of the scalpel open the spheno-parietal 

 sinus, which runs along the posterior border of the small wing of the 

 sphenoid, and trace it medially to the cavernous sinus, but do not open the 

 latter. Then remove the dura mater from the lateral part of the middle 

 fossa on one side to expose the semilunar (O.T. Gasserian) ganglion of the 

 II 14 a 



