98 ELEMENTARY BIOLOGY. [CHAP. 



c. The tJialajnencephahm : a thickened mass imme- 

 diately posterior to the cerebral hemispheres. 



Note, in connection ^vith it, 



a. The ilialaiiii opt id ; its lateral walls, consti- 

 tuting its main portion as here seen. 



^. Its ihin roof; transparent and very readily 

 torn. 



y. The pineal ghmd ; represented by a small 

 pinkish body, lying in the bay enclosed by 

 the hinder ends of the hemispheres. 



d. The optic lobes {inesencephalon) \ a pair of 

 rounded eminences lying behind the thala- 

 mencephalon. 



e. The ce7-ebelhim {metencephalon) : a narrow trans- 

 verse band next in order of succession. 



/. The vicdulla oblongata {niyelonceplialon) : 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 tlie 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 vcnt?-al aspect. 



a. The /ie?nisplieres and olfactory lobes (cf. supra). 

 The outer walls of the latter are thickened 



