VI FORM AND FUNCTION 121 
in focussing, a central eye with a very near range may 
have saved its owner occasional hard knocks against 
objects close at hand when its superior organs of vision 
were gazing upon some more distant scene. 
Of the lower parts of the brain, I do not intend 
to say much. The medulla oblongata, however (m.o. 
in Fig. 30), must not be passed over. It forms the 
lowest part of the brain, being really a continuation 
of the spinal cord. We have already seen that in it 
mainly centre the vaso-motor nerves, which govern the 
arteries and so regulate the flow of blood. And 
through it pass all of the twelve pairs of nerves 
which proceed from the brain, except two, the optic 
and olfactory; and these two are not, strictly 
speaking, nerves, but prolongations of the brain. 
The muscles that move the eyes, the muscles of 
the face, the tongue, the larynx, the lungs, the liver, 
and stomach work at the bidding of nerves that arise 
from the medulla oblongata. 
The Eye. 
In most essentials the bird’s eye is formed on the 
same plan as our own. It is a camera at the back of 
which is a nerve which expands into what is called 
the retina; the retina is sensitive to light, and the 
image formed upon it is conveyed by the nerve to the 
brain, where the impulse given to the nerve becomes 
sensation—where, that is, sight actually takes place. 
Before describing the eye more particularly, I wish 
1 For a description of the pineal body see Lubbock’s Senses 
of Animals 
