500 ELEMENTARY PHYSIOLOGY less. 



Lying beneath the hinder end of the hemisphere is a 

 large laminated mass which overhangs the posterior side 

 of the bulb and is known as the cerebellum (Cb.). When 

 the brain is removed from the skull and looked at from 

 its base or under surface many further details may be 

 at once made out. Thus it becomes evident that the 

 brain consists of two halves, corresponding to each half of 

 the spinal cord, lying symmetrically on each side of a line 

 joining GC. and M. in Fig. 160. The bulb (M) widens out 

 at its upper end and gives oft' from each side a number of 

 nerves (vii. — xii.) which are analogous to the spinal nerves 

 but, as originating from the brain, are called cranial 

 nerves. The other six pairs of cranial nerves (i. — vi.) 

 come off from parts of the brain in front of (above) the 

 bulb. The cerebellum is seen to send out from each side 

 towards the central line a large mass of transverse fibres 

 which sweep across the brain and meet, with a depression 

 in the middle line, thus forming a sort of bridge from one 

 half of the cerebellum to the other ; this bridge lies just in 

 front of (above) the bulb and is called the pons Varolii. 

 The number VI. is placed upon the pons in Fig. 160. The 

 longitudinal nerve fibres of the bulb pass forwards 

 (upwards in the figure), among and between the transverse 

 fibres of the j^oiik, and become visible again in front of it 

 as two broad diverging bundles called crura cerebri, 

 which plunge into the corresponding cerebral hemi- 

 sphere of each half of tlie brain. 



When the brain is viewed from above nothing is visible 

 beyond the convoluted surfaces of the two cerebral hemi- 

 spheres, sepai'ated b}- a median fissure whose sides are in 

 close contact. But if the sides of this fissure are cai-efully 

 pushed apart, the cerebral hemispheres may. be seen to be 

 connected with each other by an elongated transverse and 

 horizontal mass of nerve fibres known as the corpus 

 callosum (shown as CO., in Fig. 160). If the hinder 

 ends of the cerebral hemispheres are raised, the whole 

 upper surface of the cerebellum comes into view, and if 

 the cerebellum is now lifted up, the posterior surface of 



