Page:First course in biology (IA firstcourseinbio00bailrich).pdf/617



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 eyeball 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.

of right eye. (Jegi.)

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 saltish 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