84 ANATOMY OF A CHELONIAN. 



which it nearly extends ; on its dorsal aspect 

 the mesencephalon is not overlapped at all 

 by the prosencephalon. 



d. In the angle between the mid- and fore-brains, 

 the small optic thalami are seen touching one 

 another in the median line. 



e. The mesetuephalic or optic lobes {corpora bigem- 

 ina), much smaller than the prosencephalic, 

 are paired hemispherical eminences, white on 

 the surface, and placed on the dorsal side of 

 the brain. 



/. Behind the corpora bigemina, and rather lar- 

 ger than both together, is the cerebellum, only 

 attached to the rest of the brain by its anterior 

 margin, and overhanging the fore part of the 

 medulla oblongata. There is a slight notch in 

 its posterior border, from which a shallow, 

 wide median furrow proceeds forward some 

 way on its dorsal aspect. 



g. Raising the hinder part of the cerebellum, note 

 the medulla oblongata, ■^\'Ca.\h& fourth ventricle 

 on its dorsal side, tapering off posteriorly into 

 the calamus scriptorius. Note the two parallel 

 cords of white nerve-substance lying side by 

 side along the floor of the fourth ventricle ; 

 they are continuations of the anterior columns 

 of the spinal cord. 



h. On the side of the brain, note the relations of 

 the various parts already described, and trace 

 the white band of the optic tract up to the 

 mesencephalic lobe. 



i. Pushing the posterior free end of the prosen- 

 cephalic lobe out of the way on one side, di- 



