CALIFORNIA COLLEGE 

 of PmWftlACY 345 



7. If the lens cannot bring the rays of light together, a 



person is far-sighted^ but if it brings the rays to- 

 gether too soon, he is near-sighted. If it brings 

 some of the rays together sooner than others, the 

 condition is called astigmatism. 



8. If the lens does not permit light to pass through, the 



condition is called a cataract. 



9. By means of the two eyes viewing an object from 



slightly different positions, we form an idea of 



position and solidity. 

 10. If one of the muscles of the eye pulls the eyeball 



to one side, the person is cross-eyed and sees two 



objects instead of one. 

 12. Irritation of the optic nerve causes a sensation of sight 



as though light had caused the impression. Mem- 



ories of sight may be recalled so vividly as to seem 



real, as in a dream. 



DEMONSTRATIONS 



135. Examine the eyeball of a calf in its socket. Carefully sepa- 

 rate the eyeball and its muscles and nerves from the fat. Notice the 

 cushion of fat surrounding the whole eyeball. Notice the slender mus- 

 cles which arise from the back part of the orbit and are attached to the 

 outer edge of the eyeball. Notice the optic nerve entering the middle of 

 the back side of the eye. Notice other nerves and the numerous blood 

 tubes which cross the space. Preserve the specimen in Miiller's fluid. 



136. Procure several eyes removed from their sockets, and place 

 some in Miiller's fluid for a week or two, and examine others fresh. 



Notice the bulging and clear cornea, and the tough white sclerotic 

 coat. Holding the eye with its cornea toward you, cut it completely 

 into halves. Notice the aqueous and the jellylike vitreous humors. 

 Notice the curtain of the iris and its pupil. Behind the iris notice the 

 lens. Remove the lens and note its shape and its firm consistency. 

 Notice the black choroid coat lining the eyeball next to the sclerotic. 

 Notice the thin retina, which readily separates from the choroid. 



