26 DISSECTION OF THE HEAD. 



outer side of the artery. A small branch of artery to the orbit should 

 likewise be divided at this time. 



The brain is now to be supported in the left hand, and the pituitary body 

 to be dislodged with the knife from the hollow in the centre of the sphe- 

 noid bone. A strong horizontal process of the dura mater (tentorium eere- 

 belli) conies into view at the back of the cranium. Along its free margin 

 lies the small fourth nerve, which is to be cut at this stage of the proceed- 

 ing. Make an incision through the tentorium on each side, close to its 

 attachment to the temporal bone, without injuring the parts underneath ; 

 the following nerves, which will be then visible, are to be divided in suc- 

 cession. Near the inner margin of the tentorium is the fifth nerve, consist- 

 ing of a large and small root; whilst towards the middle line of the skull 

 is the long slender sixth nerve. Below the fifth, and somewhat external 

 to it, is the seventh nerve with its facial and auditory parts, the former 

 being anterior and the smaller of the two. Directly below the seventh are 

 the three trunks of the eighth nerve in one line : of these, the upper 

 small piece is the glosso-pharyngeal ; the flat band next below, the pneu- 

 mogastric ; and the long round nerve ascending from the spinal canal, the 

 spinal accessory. The remaining nerve nearer the middle line is the ninth, 

 which consists of two small pieces. 



After dividing the nerves, cut through the vertebral arteries as they 

 wind round the upper part of the spinal cord. Lastly, cut across the 

 spinal cord as low as possible, as well as the roots of the spinal nerves that 

 are attached on each side. Then on placing the first two fingers of the 

 right hand in the spinal canal, the cord may be raised, and the whole brain 

 may be taken readily from the skull in the left hand. 



Preservation of the brain. After removing some of the membranes 

 from the upper part, and making a few apertures through them on the 

 under surface, the brain may be immersed in spirit to harden the texture ; 

 and methylated spirit may be used on account of its cheapness. Placing 

 the brain upside down on a piece of calico long enough to wrap over it, 

 put it in the spirit. 



Examination of the brain. At the end of two or three days the dissec- 

 tor should examine the other membranes, and the vessels. As soon as the 

 vessels have been learnt, the membranes are to be carefully removed from 

 the surface of the brain, without detaching the different cranial nerves at 

 the under surface. The brain may remain in the spirit till the dissection 

 of the head and neck has been completed, but it should be turned over 

 occasionally to allow the spirit to penetrate its substance. 



The description of the brain and its vessels will be found after that of 

 the head and neck. 



Directions. After setting aside the brain, the anatomy of the dura mater, 

 and the vessels and nerves in the base of the skull should be proceeded 

 with. For this purpose raise the head to a convenient height, and fasten 

 the tentorium in its natural position with a few stitches. The dissector 

 should be furnished with the base of a skull while studying the following 

 parts. 



Dura mater. At the base of the cranium the dura mater is much more 

 closely united to the bones than it is at the top of the skull. Here it dips 

 into the different inequalities of the osseous surfaces ; and it sends processes 

 through the several foramina, which join for the most part the pericra- 

 nium, and furnish sheaths to the nerves. 



Beginning the examination in front, the membrane will be found to send 



