g8 ELEMENTARY BIOLOGY. [CHAP. 



c. The tlialamencephalon : a thickened mass imme- 

 diately posterior to the cerebral hemispheres. 



Note, in connection with it, 



a. The thalami optici ; its lateral walls, consti- 

 tuting its main portion as here seen. 



[5. Its thin roof; transparent and very readily 

 torn. 



y. The pineal gland ; represented by a small 

 pinkish body, lying in the bay enclosed by 

 the hinder ends of the hemispheres. 



d. The optic lobes {mesencephalon) : a pair of 

 rounded eminences lying behind the thala- 

 mencephalon. 



e. The cerebellum ^telencephalon) : a narrow trans- 

 verse band next in order of succession. 



f. The medulla oblongata ipiyeloncephalon) : the por- 

 tion of the brain lying behind the cerebellum 

 and passing into the spinal cord. Its roof is 

 covered by the choroid plexus (cf. i. b. a). 



ii. Divide the olfactory lobes, and raise the front end 

 of the brain ; turning it back gradually, divide with 

 a sharp scalpel any nerves that may be observed 

 passing from it to the cranial walls : most of these, 

 being small, will probably be torn across unob- 

 served, but the large optic nerves will at any 

 rate be seen. Remove the brain, together with 

 a small portion of the spinal cord, and examine 

 from the ventral aspect. 



a. The hemispheres and olfactory lobes (cf. supra). 

 The outer walls of the latter are thickened 



