232 THE REASON WHY. 



' Truly the light is sw eet, and a pleasant thing it is for the eyes to behold the 

 sun." ECCLESIASTES xi. 



966. Why are we enabled to see large objects upon so 

 small a surface ? 



Because the lenses and humours of the eye collect the rays of 

 light coming from every direction, and, bringing them into a focus, 

 transmit them to the retina, where each ray impresses upon the 

 nervous surface the qualities it received from the object which 

 reflected it. 



I 



Fig. 61. THE EYEBALL AND ITS MUSCLES. 



A. Portion of bone through which the optic nerve passes in its communication 

 between the brain and the eye. 



B. The optic nerve, from before which an external muscle has been cut away, 

 leaving its two attachments. 



C. The globe of the eye. 



D. The muscle which turns the eye outward, and which is counteracted by a 

 muscle on the other side. 



E. The muscle which passes through a loop, or staple of cartilage I, and turns 

 the eye obliquely. It is counteracted by a muscle situated underneath. 



F. The muscle situated underneath, which turns tlie eyeball upwards, and is 

 counteracted by 



G. The muscle which turns the eyeball downwards. 



H. The muscle attached to a bone which turns the eyeball upwards. 



I. The cartilaginous loop through which a muscle passes. 



J. The front chamber of the eye filled with a clear fluid. 



K. Fragment of the bone by which one of the muscles is fastened. 



967. Why do some persons squint ? 



Because it sometimes happens that a muscle of the eye acts too 

 powerfully for its companion muscle, and draws the eye too much 

 on one side. 



968. Why does the pupil of the eye look Hack ? 

 Because the pupil is an opening through which the rays of light 



pass into the chamber of the eye. There is, therefore, nothing in 

 the pupil, of the eye to reflect light. 



