NERVOUS SYSTEM 301 



third ventricle is formed by the crura cerebri, which extend 

 backward, between the pons and cerebellum, into the spinal 

 bulb or medulla, and this, in turn, backward into the spinal 

 cord. At the back of the third ventricle note that a tube or 

 canal (aqueduct) connects it with a much smaller cavity (the 

 fourth ventricle) just under the cerebellum. Four little 

 bodies (the corpora quadrigemina) form the roof of this tube 

 between the fornix and cerebellum. Note the tree-like inter- 

 nal structure of the cerebellum. What causes its wrinkled 

 surface? 



Note the gray and the white matter that make up the 

 cerebrum. Where is the gray matter located? the white? 



NOTE. The first ventricle in the olfactory lobes and the lateral 

 ventricle may be shown by suitable sections, if desired, and the re- 

 lation of these may be brought out by the aid of diagrams of the 

 simple brain structure. 



LXIV. DISSECTION OF SPINAL CORD. 



Apparatus. Thin section of cervical portion of spinal cord, glyc- 

 erine, slides, cover glass, compound microscope. 



Directions. (Prepare sections by placing a piece of the 

 cervical spinal cord for three or four weeks in Miiller's fluid 

 [2J parts of potassium bichromate, 1 part of sodium sulphate, 

 100 parts of water]. Then wash it with water and place it 

 in 30% alcohol for a few days. Then transfer it to 95% 

 alcohol. Cut a thin cross section and mount it in glycerine. 

 Cover it with a cover glass). 



Examine under the low power. Note the outer covering 

 of pia mater. Note the distribution of the gray and white' 

 matter. Sketch it. Is it the same as in the brain? Note 



