236 PHYSIOLOGY. 



The Cerebellum. The cerebellum is much smaller 

 than the cerebrum, and has fine transverse ridges and 

 grooves in place of the convolutions of the cerebrum. It 

 is also of a deeper color, a reddish gray. The cerebrum 

 overlaps the cerebellum so that the latter could not be 

 seen from above if the whole brain were laid bare. But 

 in the lower animals the parts of the brain are more in 

 a series, one behind the other, and in a line with the 

 spinal cord. 



The Spinal Bulb. The enlarged beginning of the 

 spinal cord, often called the medulla oblongata, is the 

 spinal bulb. It is white like the rest of the cord. 



The Brain of a Cat or Rabbit. The brain of a cat or rabbit may 

 be exposed by first mounting the specimen as directed for showing the 

 spinal cord (see p. 27). After removing the skin from the upper part 

 of the head, the bone should be cut away between the eyes with a pair of 

 bone forceps. Cautiously working backward, the whole of the brain 

 may be unroofed. Great care must be exercised, for here we have one 

 of the softest tissues of the body lying very closely beneath one of the 

 hardest. It is possible to do this with a strong knife, but the bone 

 forceps save a great deal of hard work. The bone must be broken 

 away bit by bit. To remove the brain, it will be necessary to cut 

 through the tough dura mater that covers it. 



Removing this, there will be found an inner covering, the pia mater, 

 a membrane richly supplied with blood tubes, from which the brain 

 gets its nourishment. After the dura mater has been removed, the 

 anterior end of the brain may be gently lifted with the handle of the 

 scalpel and the under surface studied, following the description of 

 the cranial nerves. 



Preservation of the Brain. 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 25 per cent. It should rest on a layer 

 of cotton, otherwise it may be very much flattened by its own weight. 

 Later transfer it to 50 per cent alcohol, and then to 75 per cent. When 

 it is well hardened, it may be sliced with a sharp scalpel as directed. 

 A better and quicker method is to use a solution of alcohol and forma- 



