300 THE HUMAN BODY. 



from the dura mater lining them. So far the specimen may be pre- 

 pared previous to the meeting of the class. 



b. To the class demonstrate the tough dura mater enveloping the 

 brain; then cut it away, noting the processes which it sends between 

 the two cerebral hemispheres and between cerebellum and cerebral 

 hemispheres. Then cut the membrane away. 



c. Note its glistening inner surface, due to the arachnoid lining 

 it; the pia mater full of blood-vessels and closely attached to the 

 brain; the glistening arachnoid layer covering the exterior of the 

 pia mater. Then put the specimen aside in alcohol for a day or 

 two. This will harden the brain substance. 



d. When the brain has become somewhat hardened dissect away 

 the pia mater on one side. Show the cerebral hemispheres and 

 their surface convolutions, the cerebellum and its foldings, the 

 medulla oblongata beneath the cerebellum. 



e. With bone forceps cut away the remainder of the sides and roof 

 of the skull. Then raise the brain in front, and cutting through the 

 vessels, nerves, etc., which attach it to the base of the skull, en- 

 tirely remove it from the skull cavity. On it demonstrate the cere- 

 bral hemispheres (which overlap the cerebellum much less than 

 in man), cerebellum, mid-brain, etc. 



f. Attached to the base of the brain will be found the stumps of 

 some of the cranial nerves, though most of these will have been en- 

 tirely torn off unless the dissector has some technical skill. The 

 optic commissure, with the optic tracts leading to it and the stumps 

 of the optic nerves leading from it, will almost certainly be found. 



g. Make sections across the brain in different directions to see the 

 gniy matter spread over most of its surface, and the nodules of gray 

 matter imbedded in its interior. 



