REMOVAL OF THE BRAIN 115 



parts of the attached border of the tentorium. The terminal 

 parts of the transverse sinuses descend along the anterior parts 

 of the lateral walls of the posterior fossa. 



Tivo sinuses run obliquely downwards, backwards, and later- 

 ally : they are the two inferior petrosal sinuses. 



Three sinuses run transversely, connecting paired sinuses of 

 opposite sides: (i) the anterior intercavernous sinus, in the 

 anterior border of the diaphragma sellae; (2) the posterior 

 intercavernous sinus, in the posterior border of the diaphragma 

 sellae ; and (3) the basilar plexus, which connects together the 

 inferior petrosal sinuses, across the upper surface of the basilar 

 part of the occipital bone. 



Alternative Method of removing the Brain. If it is thought 

 desirable to remove the brain entire, by the more rapid but less 

 instructive 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. 105). 



Remove the block upon which the head has been resting, 

 supporting the occiput and the posterior part of the brain with 

 the left hand, and 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 bulbs 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 lower surfaces 

 of the frontal lobes. As the olfactory bulbs are raised the 

 oljactory nerve filaments, which enter their lower surfaces after 

 passing 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 approaching the optic fora- 

 mina. When they are divided the internal carotid arteries will 

 be exposed. More posteriorly, in the median plane, lies the 

 infundibulum, a hollow conical process which connects the 

 hypophysis cerebri (O.-T. pituitary body] with the tuber cinereum 

 at the base of the brain ; and more laterally are the oculo- 

 motor nerves. Sever each of the structures mentioned in turn. 

 On the lateral side of each oculo-motor nerve lies the medial or 

 free border of the tentorium cerebelli, passing forwards to be 

 attached to the anterior clinoid process. Turn that margin 

 aside with the point of the knife, and the small 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 sloping process of dura mater which intervenes between 

 it and the cerebellum. Divide the tentorium along its attached 

 border, and take care whilst doing that not to injure the sub- 

 in 8 a 



