THE SENSES 



149 



intended as a blessing. Some people interpret the blessing as an 

 opportunity to do what ? 5. Name six articles which warn us to avoid 

 them by their bitter, burning, or nauseating tastes, yet which are used 

 by man. 6. Name six feelings which are intended as warnings for our 

 guidance, but which are commonly disregarded. 



The eyes on the rays of the starfish are mere spots of 

 pigment. Insects have lenses in their eyes. The eyes of 

 vertebrates are all formed on the same general plan as the 

 human eye. 



The eyeballs are globes about an inch in diameter. 

 They are placed in deep, bony sockets, called orbits, in 

 the front part of the skull. The optic nerve, other nerves, 

 and several large blood vessels pass to the eye through a 

 hole in the back of the orbit. A soft cushion of fat is in 

 the orbit behind the eyeball. A pressure upon the eye- 

 ball causes the eye to sink 

 into the socket, for the fat 

 yields to the pressure. 

 This is a protection to the 

 eye. 



The eyelids protect the 

 eyes from dust, and at 

 times from the light. They 

 are aided in this by the 

 eyelashes. 



The tears are formed by tear glands situated above the 

 eyeball in the portion of the orbit farthest from the nose, 

 just beneath the bony brow where it feels the sharpest 

 (Fig. 121). They are about the size of almonds. A salt- 

 ish liquid is continually oozing from the tear glands and 

 passing over the eyeball ; it is carried into the nose 

 through the nasal duct (Fig. 121). The tears reach this 

 duct through two small canals, which open into the eye 

 in the little fleshy elevation at the inner corners of the 



Fig. 121.— Tear Glands and 

 DUCTS of right eye. (Jegi.) 



