68 



EVOLUTION OF THE HUMAN EYE 



are much less prominent, and are separated by a consider- 

 able distance from the root of the iris (Fig. 18). 



No doubt, as has frequently been pointed out, the ciliary 

 muscle in hypermetropia, having more work to do, is hyper- 



FIG. 18. Varieties of the ciliary muscle. A, emmetropic; B, myopic; 



C, hypermetropic. (From Iwanoff.) 



trophied, while in myopia, having but little work to do, 

 it is atrophic. I think, however, the direction of its fibers 

 is largely influenced by the length of the antero-posterior 

 axis of the eyeball. Where this has been abnormally in- 

 creased, as in axial myopia, the uveal tissue is considerably 



