THE FIVE BLADDERS OF THE BRAIN, 305 
much more (Fig. G, H, Plate III.). The fourth bladder, the 
hind brain (h), forms the so-called little hemispheres, to- 
gether with the middle part of the small brain (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 jijth 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 
(Gand H) already strongly differ from that of birds (F') and of 
reptiles (Z). In the two latter the mid brain predominates, 
but in the former the fore brain. Even at this stage the 
VOL. I. x 
