212 



THE EVOLUTION OF MAN. 



gata) into the brain. The spinal marrow appears indeed to 

 be a dense mass of nervous substance; but along its axis 

 passes a very narrow canal, which is continued in front 

 into the larger cavities of the brain, and which, like those 

 cavities, is filled with a clear fluid. 



The brain forms a considerable mass of nervous sub- 

 stance, of very complex, minute structure, which occupies 



Fig. 219.— Human brain, 

 seen from the lower side. 

 (After H. Meyer.) Above (in 

 front) is the large brain 

 (cerebrum), with extensively- 

 branched furrows ; below (be- 

 hind) is the small brain (cere- 

 bellum), with narrow parallel 

 furrows. The Roman numbers 

 indicate the roots of the twelve 

 pairs of brain nerves in order 

 from front to back. 



the greater part of the skull-cavity ; it is roughly distin- 

 guishable into two main parts — the large and small brain 

 (cerebrum and cerebellum). The former is situated in 

 front and over the latter, and its surface exhibits the well- 

 known characteristic convolutions and furrows (Figs. 219, 

 220). On its upper surface it is divided by a deep longi- 

 tudinal slit into two lateral halves, the so-called "great 

 hemispheres," which are connected by means of a bridge, or 

 " cross-piece " {corpus callosum). A deep transverse fissure 

 separates the large brain (cerebrum) from the small brain 



