THE BRAIN. 85 



vide the optic tract, and trace beneath it the 

 cms cerebri passing up into the prosencephalic 

 lobe. 



209. Carefully push apart those parts of the brain 

 between which there is a median fissure, and then, with 

 a sharp, thin-bladed knife divide the whole organ, witii 

 the piece of spinal cord attached to it, in the median 

 dorso-ventral plane. On the inner surface of the sec- 

 tions note : 



a. The continuity of the fourth ventricle with the 

 central canal of the spinal cord. 



b. The form of the cut edge of the cerebellum, 

 as now exposed, which shows that that organ 

 is a thin arched lamina. 



c. The passage {aqueduct of Sylvius) from the front 

 end of the fourth ventricle to the third, and 

 the communications of this passage with large 

 cavities in the interior of the optic lobes. 



d. The third ventricle, bounded on each side pos- 

 teriorly by the flat inner surface of an optic 

 thalamus. Farther forward will be found on 

 each side an aperture (foramen of Monro) 

 leading into the lateral (first and second) cere- 

 bral ventricles, one beneath each prosencephalic 

 lobe. 



210. Make cross sections of one half of the brain 

 at different points to see the relations of the parts and 

 the distribution of white and gray matter. 



211. Now dissect the reproductive organs of your 

 present specimen (sections 121-137, ^^ ^^38-141, accord- 



