SENSE OF VISION". 

 [Fig. 174. 



409 



A Horizontal Section of the Eyeball ; 1, sclerotic coat ; 2, sheath or" the optic nerve, or canal of Fon- 

 tana; 3, circular venous sinus of the iris; 4, proper substance of the cornea; 5, arachnoidea oculi ; 6, 

 membrane of the anterior chamber of the aqueous humour ; of the two dotted lines one points to the 



35 



