INTRODUCTION 1 5 



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-bichromate (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 5% 

 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 opening 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 syringe- 

 ful of strong formal-bichromate injected into the third ventricle 

 by pushing the cannula about an inch through the infun- 

 dibulum (Fig. 103). The brain of a sheep or calf will be very 

 soft when removed, as it cannot be hardened previously by 

 injecting the hardening fluid into the arteries. Therefore it is 

 necessary to lay the specimen on absorbent cotton in the jar 

 of formal-bichromate, which must be exchanged for fresh 

 fluid on the second and third days. At least two weeks are 

 required for hardening the brain of a sheep or calf, after 

 which it is placed in 5% formalin for a week or more to wash 

 out the bichromate before dissection. Brains are best pre- 

 served permanently in 85% alcohol. The brain of the cat 

 or sheep may be satisfactorily prepared for dissection by plac- 

 ing it immediately upon removal from the skull into a 5% solu- 

 tion of formaldehyd, where it may remain until needed. 



Preparation of the Osseous System. — A mounted skeleton 

 of the cat may be purchased for about eight dollars. It is far 

 more satisfactory, however, to use the disarticulated bones for 

 study. These are easily prepared in the following manner: 

 As soon as the animal is dead, the skin and the greater part of 

 the flesh should be cut away and the internal organs removed. 



