no HEAD AND NECK 



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 

 backwards and laterally, and then ascends on the inner surface 

 of the squamous part of the temporal bone. The greater super- 

 ficial 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 an eminence called the 

 eminenlia arcuata. It runs forwards and medially and disappears 

 beneath the semilunar ganglion (Fig. 36). 



When the structures mentioned above have been found and 

 cleaned, the dissectors must remove the tentorium cerebelli. 

 Cut through the free border immediately posterior to the point 

 where it crosses the attached border ; the trochlear nerve will 

 be divided by the 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 ; 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 oculomotor nerves, and then press backwards 

 the pedunculi cerebri and the pons (Varolii), which lie immedi- 

 ately below them, to expose the trigeminal and the abducens 

 nerves. Cut the trigeminal nerves as they cross the upper 

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

 divide the small abducens nerves, which lie more medially and 

 at a slightly deeper level. Press the pons and cerebellum still 

 further back and divide the facial and acoustic nerves as they 

 enter the internal acoustic meatus. Below the acoustic nerves 

 lie the glossopharyngeal, vagus, and accessory nerves. They 

 also must be cut ; and the roots of the hypoglossal nerves, which 

 lie deeper and more medially, must be identified and divided. 

 The pons can then be displaced still further backwards and the 

 front of the medulla oblongata will be brought into view. Pass 

 the knife downwards, anterior to the medulla oblongata, into 

 the vertebral canal, and, cutting firmly backwards and laterally, 

 on each side, divide the medulla spinalis and the vertebral 

 arteries. Withdraw the knife, pass two fingers downwards, 

 anterior to the medulla oblongata, and lift it and the pons and 

 the cerebellum out of the posterior fossa. Place the lower parts 

 of the brain, which collectively constitute th hind brain, with 

 the hemispheres previously removed, and then examine the cut 

 ends of the cerebral nerves and the blood sinuses which lie in 

 the region of the posterior fossa (Fig. 36). 



In the upper end of the vertebral canal lies the upper extremity 

 of the severed medulla spinalis, attached, on each side, to the 

 margin of the foramen magnum by the uppermost dentation 

 of the ligamentum denticulatum. Anterior to the ligamentum 

 denticulatum, on each side, is the vertebral artery, and still 

 more anteriorly, on a slightly deeper plane, the fila of the anterior 



