REMOVAL OF THE BRAIN 109 



knife backwards 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 that 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. 36). 

 The dissectors will probably find that the superior sagittal sinus 

 turns to the right and becomes continuous with the right trans- 

 verse 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 that arrangement is reversed, and not uncom- 

 monly, as in the specimen shown in Fig. 36, there is a communi- 

 cation 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 

 occipital 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. 



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. Care- 

 fully dissect the lateral wall of the cavernous sinus and find in 

 it : the oculomotor nerve, dividing into two branches ; the 

 slender trochlear nerve, crossing the lateral side of the oculomotor ; 

 the ophthalmic division of the fifth and its three terminal branches 

 naso-ciliary, lacrimal, and frontal. Remove the remains of 

 the lateral wall and expose the internal carotid artery and the 

 abducens nerve (p. 234). 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 trigeminal nerve ; 

 the middle meningeal artery and its two terminal branches ; the 

 accessory meningeal artery, if it is present; and the greater 

 superficial petrosal nerve. Commence immediately to the 

 lateral side of the anterior part of the free border of the ten- 

 torium, where a cut through the inner layer of the dura will 

 open into a space between the two layers of the dura in which 

 lies the semilunar ganglion. From the postero-medial border 

 of the ganglion the sensory root passes backwards into the 

 posterior fossa to enter the pons ; and from its anterior-lateral 

 border the ophthalmic branch passes upwards and forwards in 

 the lateral wall of the cavernous sinus, the maxillary branch 

 runs forwards to the foramen rotundum, and the mandibular 

 branch passes downwards into the foramen ovale. By the 

 side of the mandibular nerve the accessory meningeal artery 

 may be found entering the cranium ; and a little further 

 posteriorly the middle- meningeal artery will be seen passing 

 into the middle fossa through the foramen spinosum. After 

 entering the cranium the middle meningeal artery runs forwards 



