416 A XA TOMICA L TECHXOL OGY. 



practiced upon dead animals, and should be done very rapidly 

 and by only three strokes of the scissors. 



If only the cephalic portion of the brain is wanted for some special purpose, the animal 

 may be pithed as directed in the Appendix ; the brain should be exposed at once so as to 

 prevent the clotting of blood about it. 



If a toad is used, it should be put into a small jar or under an " open-top " bell jar, and 

 a sponge saturated with chloroform suspended by a string near the top. In handling the 

 toad, it is well to protect the fingers with gloves or a cloth, and care should be taken not 

 to get the acrid dermal secretion into the eyes. 



1087. Injection. For the special study of the telce and plexuses, the vessels should 

 be injected. This is most conveniently done with cold flowing blue material from the 

 bulbus arteriosus ; see Appendix. 



1088. Exposure of the Frog's Brain Instruments and Ma- 

 terials. Small tray with waste paper ; bit of cloth ; arthrotome ; 

 coarse forceps ; pointed nippers ; bone scissors, not too dull ; wide 

 mouthed vial containing at least 25 cc. of 62-67 per cent, alcohol ; 

 (to 10 cc. of water add 15 or 20 cc. of 95 per cent, alcohol ; see 

 273) ; refer to some figure of the brain ( 1093). 



Fix the head by introducing the tip of the left index into the 

 mouth and applying the pollex upon the snout. With the scissors 

 or arthrotome, divide the skin between the cephalic angles of the 

 eyes. 



With the forceps, grasp the caudal cut edge of skin, and with 

 the scissors, cut the skin along a line extending approximately cau- 

 dad and just mesad of the eye and the ear (membrana tympani) on 

 each side as far as a point opposite the caudal border of the bra- 

 chium. Connect the caudal ends of the two incisions so as to remove 

 the flap. 



Grasp the left dorsal eyelid, and with the scissors cut mesad of 

 the eyeball, gradually everting it and cutting the muscles until the 

 round, white N. opticus is divided. Then cut more boldly and 

 remove the entire ball. 



From the orbit push a scissors blade through the mucosa intc 

 the mouth, and cut cephalad through the snout. Then cut caudad 

 in the same way, along the same line or a little farther laterad, a? 

 far as the skin was removed. Finally, cut from the angle of tht 

 mouth so as to remove the bony projection containing the left tym 

 panum or middle ear. 



With the nippers, tear up the muscles dorsad and laterad of thi 

 caudal part of the cranium and the first two or three vertebrae. 



Cautiously nip off the projecting border of the cranium at th 



