172 



THE HUMAN HODY. 



on the surface of the eye. This gland furnishes the 



moisture which the eye requires. 

 By winking, the moisture is 

 spread over the surface. 



7, Ordinarily moisture is sup- 

 plied only as fast as it is needed, 

 and it all evaporates. In strong 

 feelings of sorrow or joy, moist- 

 ure is poured out very rapidly, 

 and gathers in tears. Near the 

 inner angle of the eye, an open- 

 ing, apparently about as large 

 as a needle, can be seen on the 

 Fig 68 edge of each lid. These are 



LACHRYMAL APPARATUS. -1. Lach- the Openings of the ducts which 

 rymal gland. 2. Tear-passages. carry Q ff fa Q tearg rph ^j 

 3. Lachrymal eac. 4. Nasal duct. . . , . 



into a sac in the inner corner 



of the orbit (the lachrymal sac) ; and that opens into the 

 nasal duct, which runs through the lachrymal canal into 

 the nose. When tears are very abundant, they overflow 

 on the face. 



8, There are six muscles 

 attached to the eyeball. 

 One rolls it up, one down, 

 one out, one in, and two 

 roll it on an axis passing 

 from before backward. 



HOW WE SEE. 



9, The eye is like the 

 camera with which a photographer takes pictures. 



Fig. 69. 2 



MUSCLES OF THE EYE-BALL. 1. Muscle 

 of the upper lid. 2. Muscles of the ball. 

 3. Optic nerve. 



The 



SUGGESTION TO TEACHERS. Show and describe the parts of a camera. 



