214 THE EVOLUTION OF MAN. 



Skulled Animals (Craniota), from the Cyclostomi and Fishes 

 up to Man, in exactly the same form, as five bladders 

 placed one behind the other. Alike in their first rudiments, 

 they, however, differ in their further development. In Man 

 and all higher Mammals the first of these ^.ve bladders, the 

 fore-brain, develops so excessively that, when mature, it 

 forms, both in size and weight, by far the greater part of the 

 whole brain. To it belong, not only the great hemispheres, 

 but also the bridge (corpus callosum), which connects these 

 two, the olfactory lobes, from which proceed the nerves of 

 smell, and most of the processes lying on the roof and floor 

 of the great lateral cavities of the two hemispheres ; such, 

 for instance, as the large streaked bodies (corpora striata). 

 On the other hand, the "centres of sight," which lie be- 

 tween the streaked bodies, belong to the second main part, 

 which develops from the twixt-brain ; and to the same part 

 belong the third brain ventricle (which is single) and the 

 processes known as the "funnel" (infundibulum), the 

 gray mass, and the " cone " (conarium). Behind these, and 

 between the large brain and the small brain, we find a little 

 mass, composed of two pairs of bosses, and called the " four 

 bulbs," on account of two superficial furrows which cross 

 each other at right angles, thus quartering the whole mass 

 (Figs. 217, m, 218, v). Though these " four bulbs " are very 

 insignificant in Man and the higher Mammalia, they 

 constitute a distinct part of the brain, the third, or mid- 

 brain, which is, on the contrary, especially well developed 

 in the lower Vertebrates. The next or fourth part of the 

 brain is the hind-brain, or small brain (cerebellum), in the 

 strict sense of the term, with its single middle process, 

 the " worm " (vermis), and its two lateral parts, the " smalJ 



