22 4 



THE EVOLUTION Ol MAN. 



carried out in Keptiles and Birds, the other in Mammals. 

 The latter are especially distinguished by the very charac- 

 teristic development of the first section, the fore-brain. In 



FIG. 230. Brain of Babbit: A, from the dorsal side; B, from the 

 ventral side ; lo, olfactory lobnles ; I., fore-brain ; U, hypophysis at the base 

 of the twixt-brain ; III., mid-brain ; IV., hind-brain; V., after-brain; 2, optic 

 nerve; 3, motor nerve of the eye; 5-8, fifth to eighth nerves of the brain. 

 In A, the upper surface of the right large hemisphere (I.) is removed, so 

 that the streaked bodies (corpora striata) can be seen in its side chambcr 

 (ventriculus lateralis). (After Gegenbaur.) 



Mammals alone (Fig. 230) does this " great brain " develop 

 to such an extent, that it eventually covers all the other 

 parts of the brain from above. 



There are also remarkable differences in the relative- 

 positions of the brain-bladders. In the lower Skulled 

 Animals the five brain-bladders are at first situated one 

 behind the other in the same plane. If the brain is re- 

 garded from the side, a straight line may be drawn through 

 all the five bladders. But in the three higher vertebrate 

 classes, in the Amnion Animals (Amniota), a noticeable 

 curving of the rudimentary brain takes place, simultaneously 



