274 THE SPECIAL SENSES 



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. 57, 2). By this union the two eyes are enabled to act 

 harmoniously, and in some respects to serve as a double organ. 

 By reason of this same intimate 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 performs 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 function, have long made this 

 organ the subject of enthusiastic study. It is chiefly within 

 the last twenty years, however, that this study has been suc- 

 cessful 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 num- 

 ber of those who suffer from loss of sight is proportionally 

 much less than in countries where science is less known and 

 cultivated. 



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

 sight is that there are two eyes, which may either act together 

 as one, and be fixed upon one object, or one eye may be used 

 independently of the other. In consequence of this arrange- 

 ment, the loss of one eye does not necessitate blindness, and, 

 in fact, it not infrequently happens that the sight of one eye 

 may be long impaired or lost before the fact is discovered. 

 We next notice that the eyes are placed at the most elevated 



60. The two nerves constituting the pair of nerves ? 



51. Why is the eye called " the window of the soul " ? 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 ? 



