A TEXT BOOK 



YETERINARY OPHTHALMOLOGY 



INTRODUCTION. 



The visual apparatus consists of the eyeballs and 

 their accessory parts. The means of communication 

 to the brain are the optic nerves. Each eyeball 

 {Bidbus) 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 of an image in the eye. (Landois.) 



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 



