248 Life and Health 



All the parts of this most wonderful and ingenious 

 machine are arranged with such a delicate adjustment to 

 one another, and such an exquisite adaptation of every 

 part to the great object of the whole, that the eye is 

 properly regarded as one of the wonders of nature. 



385. The Eyeball and the Orbit. The eyeball is nearly 

 spherical in shape, but is slightly elongated from before 

 backwards. The front part is clear and transparent and 

 bulges somewhat prominently to allow the entrance of the 

 rays of light. 



The eye rests in a bowl- shaped socket called the orbit, 

 formed by parts of various bones of the head and face. 

 The margins of this cavity are formed of strong bone 

 which can withstand heavy blows. 



The socket is padded with loose, fatty tissue, which 

 serves as a soft and yielding bed in which the eyeball can 

 rest and move without injury. In a severe sickness this 

 fatty tissue is absorbed, and this fact explains the sunken 

 appearance of the eyes. The eye is bathed with a watery 

 fluid and protected by the eyelids and the eyebrows ; it is 

 moved in various directions by muscles, all of which will 

 be described later. 



| 386. The Optic Nerve. The orbit is pierced through its 

 posterior surface by an opening through which the nerve 

 of sight, the optic, passes to the eyeball. We may think 

 of the optic nerve holding the eyeball much as the stem 

 holds the apple. It is the function of this most important 

 nerve to transmit impressions of light to the seat of con- 

 sciousness in the brain, where they are interpreted. 

 \ 387. The Coats of the Eyeball. The eyeball proper is 

 composed of three coats, or layers, each of which performs 

 important functions. These coats are the sclerotic, the 

 choroid, and the retina. 



