THE BRAIN. 



81 



iii. The thalamencephalon is a lozenge-shaped portion 

 lying immediately behind the hemispheres and 

 between their diverging posterior ends : it is 

 covered by a thick vascular membrane — the 

 choroid plexus — over which passes the stalk of the 

 pineal body, a small body adherent to and re- 

 moved with the roof of the skull. On removing 

 the choroid plexus a slit-like hole is left in the 



O.L 



Fig. 14. The brain of the frog : dorsal surface, x 4. 



Fig. 15. The brain of the frog : ventral surface, x 4. 



C, cerebellum : CH. cerebral hemisphere : CP, choroid plexus of third 

 ventricle : F, fourth ventricle : IN, tuber cinereum : M, medulla oblongata, 

 O, olfactory lobe : OC, optic chiasma : OL, optic lobe : P, stalk of pineal 

 body : PB, i:)ituitary body : T, thalamencephalon. 



I, olfactory nerve : ll, optic nerve : III, third or motor oculi nerve : 

 IV, fourth nerve : V, fifth or trigeminal nerve : VI, sixth nerve : VII, 

 and VIII, combined root of facial and auditory nerves : IX and X, 

 combined root of glossopharyngeal and pneumogastric nerves. 



roof of the thalamencephalon through which the 

 vessels of the plexus pass into the third ventricle, 

 or cavity of the thalamencephalon. The thickened 

 sides of the thalemencephalon are the optic 

 thalami. 

 iv. The optic lobes are a pair of prominent ovoid bodies 

 G 



