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. 1 



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 arc 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 actual ly takes place. 



Before describing the eye more particularly, I wish 



1 For a description of the pineal body see Lubbock's Se?ises 

 pf Animah 



