6 



VETERINARY OPHTHALMOLOGY. 



the top of which is placed a box or lantern containing a 

 convex lens and sloping mirror, or a prism combining 

 the lens and mirror. The rays of light from surrounding 

 objects are received by the lens, and the mirror reflects 

 images of the scenery downwards on a table placed 

 underneath (invented by Batista Porta in the end of the 

 16th century). Now the light passes through the 

 cornea, aqueous humor, lens and vitreous humor, and is 

 focussed on the retina. The retina appreciates both 

 intensity and color. Images which are formed on the 



Fig. 2.— Scheme of accommodation. (Lnndois.) 



The right side of the figure represents the condition of the lens during ac- 

 commodation for a new object, and the left side when the eye is at rest. 

 The letters indicate the same parts on both sides ; those on the right 

 side are marked with a stroke. A, left, B, right half of the lens : C, 

 cornea ; S, sclerotic ; OS, canal of Schlemm ; VK, anterior chamber ; J, 

 iris ; P, margin of the pupil ; V, anterior surface ; H, posterior surface 

 of the lens ; R, margin of the lens ; F, margin of the ciliary processes ; 

 A B, space between the two former ; the line Z X indicates the thick- 

 ness of the lens during accommodation for a near object ; Z Y tha 

 thickness of the lens when the eye is passive. 



retina are inverted. (Fig. 1.) These impressions are 

 conveyed to the brain by the optic nerves, and thence 



