lS2 



THE FROG 



coat of the concealed portion of the eyeball is the sclerotic 

 (Scl), 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 



e.c. fi. 



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

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

 ciliary processes ; £. c, e. cj. conjunctiva ; /. iris ; L. lens ; O.N. optic nerve ; os. 

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

 retina; p.c.R. anterior non-visual portion of retina; /*ir. pigmented epithe- 

 lium (black); R. retina; Scl. sclerotic; .?//. suspensory ligament of lens; 

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



nerve (O.N). 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 (/), with 

 a black spot— really a hole — in its centre, l\\ft pupil. 



