l82 



THE FROG 



coat of the concealed portion of the eyeball is the sclerotic 

 {Set), and is formed of cartilage in the frog ; its dark colour 

 is due to the presence of a layer of black pigment which 

 forms one of the internal coats ; this will be referred to here- 

 after. Entering the sclerotic on its inner side, i.e., the side 

 next the braincase, will be seen the cut end of the optic 



Fig. 57. — Diagrammatic horizontal section of the human eye. 

 . cornea ; Ch. choroid (dotted) ; C.P. radiating folds of the choroid, known as the 

 ciliary processes ; e. c, e. cj. coiyunctiva ; /..iris ; L. lens ; O.N. optic nerve ; as. 

 ora serrata, a wavy line forming the boundary of the visual portion of the 

 retina; p.c.R. anterior non-visual portion of retina; PE. pigmented epithe- 

 lium (black) : R. retina ; Scl. sclerotic ; Spl. suspensory ligament of lens ; 

 V. H. vitreous chamber. (From Foster and Shore's Physiology^ 



nerve (O.JV). The transparent, exposed portion of the 

 eyeball is the cornea (c), a superficial thin layer of which, or 

 conjunctiva (e.c, e. cj.), is continuous with the lining of the 

 eyelids and thus with the skin covering the head ; through 

 it can be seen the coloured part of the eye, or iris (I), with 

 a black spot — really a hole — in its centre, the pupil. 



