THE BRAIN. 453 



Cut away, hit by bit, the roof and sides of the shull, luith 

 the scalpel and stout scissors, so as to expose the brain 

 thoroughly, leaving one ear uninjured. Bemove the neural 

 arcJus of the first two vertebra, and divide the spinal cord 

 transversely. Turn out the brain carefully, cutting across the 

 several nerve-roots one by one. Place the brain in a bottle of 

 strong spirit, with a pad of loose cotton-ivool at the bottom, 

 and leave it for two or three days imtil it is thoroughly 

 hardened. Examine it in weak spirit. 



B. External Characters of the Brain. 



1. The dorsal surface, 



a. The cerebral hemispheres are a pair of large pyri- 



form bodies, closely applied to each other in the 

 median plane. Their surfaces are nearly smooth, 

 and their anterior ends bluntly pointed. 



b. The olfactory lobes are a pair of small conical bodies, 



projecting forwards from the anterior ends of the 

 hemispheres. 



c. The pineal body is a small oval body, immediately 



behind the hemispheres, and in the angle between 

 them. 



d. The optic lobes are a pair of smooth ovoid bodies 



at the sides of the brain, behind and rather below 

 the hemispheres. 



e. The cerebellum is a median elongated oval body, 



marked by a number of transverse fissures. In 

 front it is in contact with the hemispheres ; 

 behind, it overlaps the medulla ; and laterally, 

 it lies above the optic lobes. 



f The medulla oblongata is thick and wide : its an- 

 terior end is covered by the cerebellum, and pos- 

 teriorly it is continuous with the spinal cord. 



2. The ventral surface of the brain. 



a. The optic chiasma, formed by the crossing of the 



