Mammalia. 



149 



with the handle of the scalpel and the under surface studied, 

 following the directions in finding the cranial nerves. 



The brain may be studied while it is fresh, but it is more 

 easily handled after it has been hardened. Lay the brain in 

 weak alcohol, about twenty-five per cent. It should rest on a 

 layer of cotton, otherwise it may be very much flattened by its 

 own weight, and get a good deal out of shape. Later transfer 

 it to fifty per cent alcohol, and then to seventy-five per cent ; or 

 use a solution of alcohol and formalin as follows : ninety-five 

 per cent alcohol, sixty parts ; two per cent formalin, forty parts. 

 The liquid need not be changed if used in sufficient volume. 

 When it is well hardened, it may be sliced with a sharp scalpel 

 as directed. 



The Brain of the Rabbit (Alcoholic Specimen). The brain of a 

 cat or dog is better, being larger. Take a brain well hardened, 

 and review the parts as named above. It is very desirable to 

 have a specimen in which the arteries have been injected. 



1. Press down the cerebellum, to see the deep groove between 

 it and the cerebrum. The thin membrane covering the brain 

 and dipping into the grooves is the pia mater. 



2. Press down the spinal bulb and tear away the pia mater 

 where it passes from the cerebellum to the spinal bulb. Note, 

 between the bulb and the cerebellum, a space covered by a thin 

 membrane. Cut into this membrane ; the cavity is the fourth 

 ventricle of the brain. Observe the two ridges bounding the 

 sides of the fourth ventricle. At the point of their divergence, 

 observe the opening of the central canal of the spinal cord. 



3. Gently separate the cerebral hemispheres, and note the 

 transverse band of white fibers connecting them. 



4. Examine the under surface of the brain, and find the roots 

 of the cranial nerves. 



The Cranial Nerves. i. The olfactory lobes (probably cut or 

 broken off) extend forward from the fore part of the cerebral 

 hemispheres. 



2. Note that the optic nerves join each other before reaching 



