1 82 



THE FROG 



portion of the eyeball is the sclerotic (Set), and is formed of 

 cartilage in the frog ; the 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 hereafter. Entering the 

 sclerotic on its inner side, i.e., the side next the brain-case, 

 will be seen the cut end of the optic nerve (O.N). The 



ecf 



So) 



FIG. 57. Diagrammatic horizontal section of the human eye. 



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

 ciliary processes ; e. 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 ;/. c. R. non-visual portion of retina ; PE. pigmented epithelium (black) ; 

 *R. retina ; Scl. sclerotic ; spl. suspensory ligament of lens ; V. H. vitreous 

 chamber, (From Foster and Shore's Physiology.} 



transparent, exposed portion of the eyeball is the cornea (c\ 

 a superficial thin layer of which, or conjunctiva (e.c., e. cf), 

 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, the pupil. 



