THE VERTEBRATE EYE. 



121 



an image of ah c will be thrown on a screen or on a 

 retina at a' b' c'. The image, it will be observed, is 

 necessarily reversed. This is the form of eye which 

 we possess ourselves ; it is, in fact, a camera obscura. 

 It is that of all the higher animals, of most molluscs, 

 the ocelli of insects, etc. 



Fig. 77, taken from Helmholtz, will give an idea of 

 the manner in which we see. 



Fig. 7 r._(?, Vitreous humor; L, lens; W, aqueous humor; c, ciliary process; d, 

 optic nerve ; e e, suspensory ligament ; k Ic, hyaloid membrane ; //, h h, cornea ; 

 g g, choroid ; i, retina ; 1 1, ciliary muscle ; mf, nf, sclerotic coat ; p p, iris ; s, 

 the yellow spot. 



The eyeball is surrounded by a dense fibrous mem- 

 brane, the sclerotic coat, or ivhite of the eye, mf, nf which 



