10 ELEMENTS OF MAMMALIAN ANATOMY. 
Preparation of the Central Nervous System.—The 
animal may be killed either with chloroform or ether. 
About 200 c.c. of formal-bichromate (170 c.c. of 5% 
potassium bichromate and 30 c.c. of formalin) are then 
injected slowly craniad into the carotid artery (Figs. 3, 4, 
and 5). After skinning, the eyes should be cut out and the 
flesh removed from the head and dorsal side of the vertebral 
column. On a line connecting the caudal borders of the 
orbits, cut through the skull to the brain with the bone 
cutters and remove piece by piece the roof of the skull. 
Next cut away the lateral walls down to the base of the 
brain. Care must be exercised in laying bare the cere- 
bellum, and cutting loose the tertorium cerebelli, the plate 
of bone separating the cerebrum from the cerebellum. The 
spinal cord is next laid bare dorsally, beginning with the 
atlas, by cutting through the pedicles of the neural arches 
on either side. With a sharp knife or a pair of scissors 
the spinal nerves may then be cut and the cord lifted from 
behind forward out of its bed, until the brain is reached. 
The latter must be carefully raised while the nerves at its 
base are cut, and the dura mater loosened. 
The brain is firm enough to dissect as soon as removed, 
but it is better to further harden it and differentiate the 
white and gray matter by placing it in weak formal-bichro- 
mate (5% formalin, 500 c.c.+5% potassium bichromate, 
500 c.c.) one week in the dark. Light causes a precipitate. 
At the end of one week the specimen should be placed in 
1000 c.c. of §% formalin for another week, after which it 
is ready for dissection. In case brains of calves or sheep 
are used a hammer and bone chisel are necessary for open- 
ing the skull. The head should first be nailed to the tray. 
As soon as the brain is removed it should be placed in a 
large pan of water and the dura mater carefully cut away, 
the clotted blood washed off and a syringeful of strong 
