2i2 HEAD AND NECK 



fifth nerve, the middle meningeal artery and its two terminal branches, the 

 accessory meningeal artery, if it is present, and the great superficial petrosal 

 nerve. Commence immediately to the lateral side of the anterior part of 

 the free border of the tentorium, where a cut through the inner layer of the 

 dura will open into a space (O.T. Meckel's cave) between the two layers of 

 -the dura, in which lies the semilunar ganglion. From the postero-medial 

 border of the ganglion the posterior branch or sensory root passes backwards 

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

 the ophthalmic branch passes upwards and anteriorly in the lateral wall of 

 the cavernous sinus, the maxillary branch runs anteriorly to the foramen 

 rotundum, and the mandibular branch passes downwards into the foramen 

 ovale. By theside of the mandibular nerve the accessory meningeal artery may 

 be found entering the cranium ; and a little further posteriorly the middle men- 

 ingeal artery will be seen passing into the middle fossa through the foramen 

 spinosum. After entering the cranium the middle meningeal artery runs 

 anteriorly and laterally, across the floor of the middle fossa, towards the 

 lateral wall and divides into an anterior and a posterior branch ; the former 

 ascends on the anterior part of the lateral wall to the anterior inferior angle 

 of the parietal bone, and the latter runs posteriorly and laterally, and then 

 ascends on the inner surface of the squamous part of the temporal bone. 

 The great sitperficial petrosal nerve appears on the anterior surface of the 

 petrous part of the temporal bone through the hiatus nervi facialis, which 

 lies to the medial side of the eminentia arcuata. It runs anteriorly and 

 medially and disappears beneath the semilunar ganglion. 



After the structures mentioned above have been found 

 and cleaned, the dissectors must remove the tentorium cere- 

 belli. Cut through the free border immediately posterior to 

 the point where it crosses the attached border; the fourth nerve 

 also will be divided by this incision. Repeat the incision on 

 the opposite side, and then cut through the membrane close 

 to its attached border, but to the medial sides of the superior 

 petrosal and transverse sinuses ; next divide the venae basales 

 at their points of junction with the vena cerebri magna 

 (O.T. vein of Galen); then raise the anterior part of the 

 tentorium and, passing the knife beneath it, separate it from 

 the falx cerebelli, which is attached to its lower surface in the 

 median plane. The tentorium may now be lifted out and the 

 arachnoid covering the upper surface of the cerebellum will 

 be exposed. 



After the upper surface of the cerebellum has been cleaned, 

 cut through the third cerebral nerves, and then press back- 

 wards the pedunculi cerebri and the pons (Varolii), which lies 

 immediately below them, to expose the fifth and the sixth 

 nerves. Cut the fifth nerves as they cross the upper borders 

 of the petrous parts of the temporal bones, and then divide 

 the small sixth nerves, which lie more medially and at a 

 slightly deeper level. Press the pons and cerebellum still 



