RAT. 61 



folds (vocal chords), which narrow the opening. Insert a 

 probe into the glottis. Where does it appear? 



Split the skin down the back and remove it from the 

 body, and then with the bone forceps break through the 

 cranial walls at the back of the head,* taking pains not to 

 injure the underlying structures. When the opening is 

 made enlarge it by removing the skull bit by bit with a 

 strong knife from the dorsal surface and right side. Then 

 continue the process back in the neck region as far as the 

 shoulders until the brain and anterior part of the spinal 

 cord are exposed. 



In the brain, viewed from above, make out in front the 

 olfactory lobes, next the large cerebrum, and behind this 







the cerebellum, and following the cerebellum the medulla 

 oblongata, broad in front and tapering behind into the 

 spinal cord. Are any of these parts paired? The line 

 between medulla and spinal cord is not a sharp one, and 

 the place of passage through the skull may be regarded as 

 the boundary. Sketch these parts in outline from above 

 and from the side, X2. 



Over the whole brain is a rather tough membrane, the 

 dura mater, which is next to be removed from the dorsal 

 surface. Do you find any convolutions on the cerebrum? 

 Cut through the olfactory lobes as far forward as possible 

 and lift the cerebrum very carefully from in front. It 

 will be found to be tied by the optic nerves, going from 

 the ventral surface. Cut these as close to the skull as pos- 



* The points relating to the brain can be made out more easily on 

 the cat or sheep, but with a little pains the directions here given can 

 be followed on the rat. In the case of these larger forms the brain- 

 cavity should be opened and the whole head be placed in some 

 hardening fluid (Miiller's fluid, formol, or alcohol) some days before 

 the laboratory exercises. 



