44 



A. Not exactly. The front projects beyond the 

 general curvature. The effect is, the compass of 

 our vision is enlarged, and we can see further around 

 us, than if this part of the eye were not so protu- 

 berant. 



B. What a multiplicity of provisions for the per- 

 fection of this beautiful and noble organ. 



Fig. 6. 



e, aqueous humor, t, t, iris, o, pupil. d, chrystaline humor. 

 e } e, vitreous humor. A, a, rays of light crossing at the pu- 

 pil, and passing from the object A, A, to form the image on 

 the retina, a, a. /, optic nerve. 



T. In speaking of the pupil, do you remember 

 what is stated as to the contrivance by which it is al- 

 ways kept in a round form ? 



A. The constant exactness of the circle, notwith- 

 standing its changing its dimensions almost every mo- 

 ment, has been always mentioned as a curious phe- 

 nomenon. No artist would find it easy to imitate this 

 contrivance. It has been supposed to be effected by 

 means of fibres or threads in the iris, so arranged with 

 reference to the central opening as to enlarge or con- 

 tract it like a purse ; though some anatomists are not 

 entirely satisfied how it is produced. They say the 



