400 



ELEMENTARY PHYSIOLOGY 



LESS 



denser, and capal)le of refracting light more strongly 

 than either of the humours. The crystalline lens is com- 

 posed of fibres having a somewhat complex arrangement, 



Pio. 126.— Horizontal Section of the Eyeball. 



1, cornea; 1', coiijunctiva ; 2, sclerotic; 2', sheath of optic nerve; 

 3, choroid ; 3", rods and cones of tlie retina ; 4, ciliary muscle ; 4', cir- 

 cular portion of ciliary muscle ; T), ciliary process ; G, posterior chamber 

 between 7, the iris and the suspensory ligament ; 7', anterior chamber ; 

 S, artery of retina in the centre of the optic nerve ; 8', centre of blind 

 spot ; 8", macula lutea ; 9, ora scrrata (this is of course not seen in a 

 sei'tion such as this, but-is introduced to show its position) ; 10, space 

 behind the suspensory ligament (canal of Petit); 12, crystalline lens ; 

 13, vitreous humour; 14, marks the position of the ciliary ligament; 

 a a, optic axis ; b h, line of equator of the eyeball. 



and is highly elastic. It is more convex behind than in 

 front, and it is kept in place by a delicate, but at the 



