THE SENSE OF SIGHT 



399 



sympathetic impulses conveyed to the secreting cells 

 by way of the sympathetic filaments from the sym- 

 pathetic system in response to emotional states from 

 the brain centres. The tears consist of water and 

 inorganic salts. The secretion leaves the gland by 

 way of seven or eight ducts and bathes the corneal 

 surface of the eye during the act of winking, thus 

 moistening the eye and removing foreign bodies. 

 It then passes into the lacrymal duct to drain into the 



FIG. 140 



The lacrymal apparatus. (Gray.) 



nasal cavity. An excess secretion, as is observed in 

 weeping, or due to a foreign body in the conjunctiva, 

 passes over the lower lid and drains down the cheek, 

 as well as the nasal cavity. 



The Eye-ball. This consists of three coats enclosing 

 the refractive media or humors. They are the sclerotic 

 and cornea outside, the retina internally, and the 

 choroid between the sclerotic and retina. 



The sclerotic coat is a dense fibrous membrane, white 



