THE FIVE BLADDERS OF THE BUAIN. 305 



much more (Fig. G, H, Plate III.). The fourth bladder, the 

 kind brain (h), forms the so-called little hemispheres, to- 

 gether with the middle part of the small Wain (cerebellum), 

 a part of the brain as to the function of which the most con- 

 tradictory conjectures are entertained, but which seems prin- 

 cipally to regulate the co-ordination of movements. Lastly; 

 the fifth bladder, the after brain (n), develops into that 

 very important part of the central nervous system which 

 is called the prolonged marrow (medulla oblongata). It 

 is the central organ of the respiratory movements, and of 

 other important functions, and an injury to it immediately 

 causes death, whereas the large hemispheres of the fore brain 

 (or the organ of the " soul," in a restricted sense) can be re- 

 moved bit by bit, and even completely destroyed, without 

 causing the death of the vertebrate animal — only its higher 

 mental activities disappearing in consequence. 



These five brain bladders, in all vertebrate animals which 

 possess a brain at all, are originally arranged in the same 

 manner and develop gradually in the different groups so 

 differently, that it is afterwards very difficult to recognize 

 the corresponding parts in the fully-developed brains. In 

 the early stage of development which is represented in 

 Fig. 7, it seems as yet quite impossible to distinguish the 

 embryos of the different mammals, birds, and reptiles, from 

 one another. But if we compare the much more developed 

 embryos on Plates II. and III. with one another, we can 

 clearly see an inequality in their development, and especi- 

 ally it will be perceived that the brain of the two mammals 

 (fi and H) already strongly differ from that of birds {F) and of 

 reptiles {E). In the two latter the mid brain predominates, 

 but in the former the fove brain. Even at this sta^xe the 



