304. THE HISTORY OF CREATION. 
Fic. 7.—Embryo of a mammal or bird, in 
which the tive brain-bladders have just com. 
menced to develop. v. Fore brain. z. Twixt brain. 
m. Mid brain. h. Hind brain. n. After brain. 
p. Spinal-marrow. a. Hye-bladders. w. Primi- 
tive vertebra. d. Spinal-axis or notochord. 
The first bladder, the fore brain (a), 
is in so far the most important that 
it principally forms the hemispheres of 
the so-called larger brain (cerebrum), 
that part which is the seat of the 
higher mental activities. The more 
these activities are developed in the 
series of vertebrate animals, the more 
do the two lateral halves of the fore 
brain, or the hemispheres, grow at the 
expense of the other bladders, and 
overlap them in front and from above. In man, where they 
are most strongly developed, agreeing with his higher men- 
tal activity, they eventually almost entirely cover the other 
parts from above (compare Plates II. and III.) The second 
bladder, the twiat brain (2), forms that portion of the 
brain which is called the centre of sight, and stands in 
the closest relation to the eyes (a), which grow right and 
left out of the fore brain in the shape of two bladders, and 
later lie at the bottom of the twixt brain. The third bladder, 
the mid brain (m), for the most part vanishes in the 
formation of the so-called four bulbs, a bossy portion of 
the brain, which is strongly developed in reptiles and 
birds (Fig. #, F, Plate II.), whereas in mammals it recedes 
