A TEXT BOOK 



VETEEINARY OPHTHALMOLOGY 



INTRODUCTION. 



The visual apparatus consists of tlie eyeballs and 

 their accessory parts. The means of communication 

 to the brain are the optic nerves. Each eyeball 

 {Bulbus) forms a hollow spherical box, blackened in- 

 teriorly, with a system of convex lenses, in front, for 

 forming images of external objects, and the retina 

 behind, which is the perceptive membrane/ The whole 



Fig. 1.— Formation o£ an image in the eye. (iandois.) 



By following the rays from the object A B, It may be seen that they are 

 brought to a focus on the retina, where a small inverted image is 

 formed. 



is likened to a camera obscura. A camera obscura is an 

 optical apparatus, consisting of a darkened chamber, at 



