32 LESSONS IN HORSE JUDGING. 



this again the lens D. I. with its muscle, the ciliary 

 muscle (D 2.) 



Let us describe the remainder of the e3^e by the 

 aid of the lower diagram we are now looking at. 

 That very large space marked F^is filled by a 

 transparent jelly-like substance called the vitreous 

 humour. Then you see the nerve of sight as it 

 comes from the brain (D, o n) piercing the back 

 of the white outer tunic like the end of a lead pencil, 

 and when it has gained the inner part of the tunic 

 it spreads out like a sheet of tissue paper, and lines 

 the back of the white tunic inside and is known as 

 the ' retina ' (D R). In this thin filmy sheet or 

 ' retina,' close to the optic nerve, is a little body 

 called the yellow spot [D Y S). 



26.— So much for the eyeball. Now let us see 

 how it is moved. The eyeball is imbedded in the 

 bony skull in a socket or case, partly of bone, called 

 the ' orbit,' and being very delicate, this bony orbit 

 is filled with fat, (Fig. 5, D), in which the eyeball is 

 imbedded. In old horses and during illness this 

 fat wastes away and allows the eyeball to sink in its 

 socket. There are five or six muscles, (Fig. 5, m m) 

 to move the eye. The ends of each muscle are at- 

 tached, one to the bony socket the other to the white 

 outer tunic. We have only two of these muscles 

 depicted in the diagram, but in real life one muscle 

 is attached to the upper part of the eye ; one to the 

 lower ; one to the inner or nose side ; one on the 

 outer side. So that when the top one contracts the 



