218 HEAD AND NECK 



method usually adopted in the post-mortem room, then the following steps 

 should be taken after the falx cerebri has been detached from the crista 

 galli and the dura mater lining the vault of the cranium has been thrown 

 aside (see p. 204). 



Remove the block upon which the head has been resting, and, support- 

 ing the occiput and the posterior part of the brain with the left hand, let 

 the head drop well downwards and in all probability the weight of the 

 frontal lobes will draw them away from the floor of the anterior fossa of 

 the skull, and possibly the olfactory^ lobes may be carried with them. If 

 the olfactory bulbs remain in position on the cribriform plates of the 

 ethmoid at the sides of the crista galli, gently raise them with the handle 

 of the scalpel and press them backwards on to the under surfaces of the 

 frontal lobes. As the olfactory bulbs are raised the olfactory nerve fila- 

 ments which pass from their lower surfaces through the cribriform plates 

 are torn. As the frontal lobes are pressed backwards the large round 

 and white optic nerves come into view as they are leaving the cranial cavity 

 through the optic foramina. When these are divided the internal carotid 

 arteries will be exposed, and more posteriorly in the median plane lies the 

 infundibulum , a hollow conical process which connects the hypophysis 

 cerebri (Q.T. pituitary body] with the tuber cinereum at the base of the 

 brain, and more laterally are the oculo-motor nerves. Sever each of these 

 structures in turn. On the lateral side of each third nerve lies the medial 

 or free border of the tentorium cerebelli passing anteriorly to be attached to 

 the anterior clinoid process. Turn this margin aside with the point of the 

 knife, and the minute trochlear nerve (fourth cerebral nerve) will be brought 

 into view. It lies under shelter of the free border of the tentorium, and 

 should be divided at this stage. The head must in the next place be turned 

 forcibly round, so that the face is directed over the left shoulder. Raise 

 the posterior part of the right cerebral hemisphere with the fingers, and 

 note that it rests upon the tentorium cerebelli a broad horizontal process 

 of dura mater which intervenes between it and the cerebellum. Divide 

 the tentorium along its attached border, and take care whilst doing this 

 not to injure the subjacent cerebellum. Now turn the head so as to bring 

 its left side uppermost, and treat the tentorium on that side in the same 

 manner. The two parts of the trigeminal nerve (fifth cerebral nerve) per- 

 forating the dura mater near the apex of the petrous portion of the temporal 

 bone ; the abducent nerve (sixth cerebral nerve) piercing the dura mater 

 behind the dorsum sellae of the sphenoid bone ; the facial nerve and the 

 acustic nerve disappearing into the internal acustic meatus ; the glosso- 

 pharyngeal, the vagus, and the accessory nerves leaving the skull through 

 the jugular foramen ; and the two slips of the hypoglossal nerve piercing the 

 dura mater over the hypoglossal canal (O.T. anterior condyloid foramen), 

 will each in turn come into view upon either side, and must be divided in 

 succession. In the case of the three nerves passing out of the cranium 

 through the jugular foramen, the dissector should endeavour to leave the 

 accessory of the right side intact within the cranium, by dividing its roots 

 of origin from the medulla oblongata. whilst on the other side he should 

 remove it with the brain. This nerve is readily recognised because it 

 ascends from the vertebral canal into the cranial cavity through the foramen 

 magnum. Now thrust the knife into the vertebral canal, and divide the 

 medulla spinalis and the vertebral arteries, as they turn anteriorly upon 

 the upper part of the medulla spinalis (O.T. spinal cord) ; then sever the 

 accessory nerve of the left side, and the roots of the first pair of spinal 

 nerves. When this has been done let the head fall well downwards, gently 

 dislodge the medulla oblongata and cerebellum, and the whole brain can 

 be removed. The vena cerebri magna (Galen), as it passes from the 



