STRUCTURE OF NERVES. 33 



here we have one of the softest of the tissues of the body 

 lying very closely beneath one of the hardest. It is possible 

 to do this work with a strong knife, but the bone forceps save 

 a vast amount of extra work. The bone must be broken away 

 bit by bit. 



Compare the color of the brain with that of the spinal cord. 



The tough membrane covering the brain is the Dura Mater, 



The fore part of the brain is the Cerebrum. Note the 

 groove separating it into the right and left Hemispheres. Ob- 

 serve the ridges, or Convolutions, of its surface. The prolon- 

 gations of the brain between the eyes are the Olfactory Lobes. 



Back of the cerebrum is the Cerebellum. Look at the 

 human skull to see whether there is a bony partition corre- 

 sponding to that which separates the cerebrum from the 

 cerebellum in the rabbit. 



The widening part of the spinal cord within the skull is 

 the Spinal Bulb (Medulla Oblongata). 



Make a drawing of the brain and spinal cord, showing as 

 many as possible of the points above noted. If desired, the 

 brain and cord, with a short part of each nerve, may be re- 

 moved from the body, and laid on a cushion of cotton in weak 

 alcohol. 



Structure of Nerves and Nerve Fibers. When we 

 trace the sciatic nerve outward, we find that it is continually 

 subdividing. This dividing goes on until the branches are 

 too small to be seen by the naked eye. Microscopic examina- 

 tion shows that a nerve is made up of a great number of 

 fibers bound together in a 'common sheath of connective tis- 

 sues very much the same as in a muscle. When the nerve 

 divides it is found that, ordinarily, there is no true branching, 

 or forking, but that certain of the fibers have simply sepa- 

 rated from the rest, as in the separation of the fibers in floss 

 silk. 



