198 THE SPECIAL SENSES. 



to no other impression than that of light, and it is the only 

 nerve which is acted upon by this agent. The optic nerve, 

 also called the " second pair" of cranial nerves, is the means 

 of communication between the eye and the brain. 



50. The two nerves constituting the pair, arise from 

 ganglia lying at the base of the cerebrum, one of them on 

 each side; from which points they advance to the eyes, 

 being united together in the middle of their course in the 

 form of the letter X (Fig. 43 2). By this union the two 

 eyes are enabled to act harmoniously, and in some respects 

 to serve as a double organ. And by reason of this same in- 

 timate nervous communication, when serious disease affects 

 one eye, the fellow-eye is extremely liable to become the 

 seat of sympathetic inflammation; and this, if neglected, 

 almost certainly results in hopeless blindness. 



51. The Organ of Sight. The Eye. The proximity 

 of the eye to the brain, and the important part it per- 

 forrfis in giving expression to the emotions, have given it 

 the name of "the window of the soul." The exceeding 

 beauty of its external parts, and the high value of its func- 

 tion, have long made this organ the subject of enthusiastic 

 study. It is chiefly within the last twenty years, however, 

 that this study has been successful and fruitful of practical 

 results. Several ingenious instruments have been invented 

 for the examination of the eye in health and disease, and 

 new operations have been devised for the relief of blindness 

 and of impaired vision. As a result, it is now a well- 

 marked fact that, in civilized lands, the number of those 

 who suffer from loss of sight is proportionally much less 

 than in countries where science is less known and culti- 

 vated. 



52. The most obvious fact in respect to the apparatus of 



5O The two nerves constituting the pair of nerves ? 



51. Why is the eye called the ' window of the soul? 11 Why, the subject of 

 enthusiastic study ? 



52. The most obvious fact? The consequence? The next thing noticed? 

 Its range of view ? Of what does the organ of vision consist ? 



