266 THE ANATOMY OF THE HORSE. 



hiimour. It passes over the rim of the lens, and blends with the 

 anterior part of the lens-capsule. Behind the rim of the lens thi 

 ciliary processes rest on the outer surface of the ligament ; and whei 

 these are removed, the ligament is there seen to have a fluted or plaitec 

 appearance, each plait fitting into the depression between two processes 

 At this same point the inner surface of the zonula forms the oute: 

 boundary of a triangular chink which runs round the lens behind iti 

 rim. This is the canal of Petit, which is bounded in fro» by the lens 

 capsule, behind by the hyaloid membrane of the vitreous humour, anc 

 outwardly by the zonula. 



Structure. — When removed from its capsule, the lens is found to b( 

 soft and pulpy in its outer portion, but its density increases in passing 

 from the surface to the centre. Both its surfaces show some faim 

 white lines radiating from the central point of the surface. Tl^e numbei 

 of these lines varies in the adult, but in the foetus they are' three ii 

 number, and each lin,e on the posterior surface is in position midwa] 

 between two of the anterior lines. 



A lens that has been hardened in spirit or by boiling may be broker 

 down into concentric laminae like the coats of an onion. Each of thes( 

 laminse is composed of long riband-shaped fibres. These lens-fibres whei 

 examined microscopically are seen to have finely serrated edges b] 

 which adjacent fibres are interlocked. 



The foetal lens is nearly spherical, it is of a reddish colour, and no' 

 quite transparent. In the young adult it is distinctly biconvex, firm 

 colourless, and transparent. With advancing age it tends to becomi 

 flatter, denser, less transparent, and of a yellowish colour. 



The ViTBBOUs HuMODR occupies four-fifths of the interior of the eye 

 ball. It is globular in form, with a depression in front for the lodgmen 

 of the lens. It is colourless, transparent, and of a consistency like thii 

 jelly. It is enveloped by a delicate capsule — the hyaloid membrane, whic] 

 is connected in front with the suspensory ligament of the lens, and end 

 by joining the capsule behind the lens. 



Structure. — The vitreous humour is composed of branched connective 

 tissue corpuscles in a jelly-like matrix. 



