266 THE ANATOMY OF THE HORSE. 



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

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

 ciliary processes rest on the outer suxface of the ligament ; and when 

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

 appearance, each plait fitting into the depression between two processes. 

 At this same point the inner surface of the zon\ila forms the outer 

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

 rim. This is the canal of Petit, which is bounded in front by the lens- 

 capsule, behind by the hyaloid membrane of the vitreous humoiu-, and 

 outwardly by the zonula. 



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

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

 from the sui-face to the centre. Both its surfaces show some faint 

 white lines radiating from the central point of the surface. The number 

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

 number, and each line on the posterior surface is in position midway 

 between two of the anterior lines. 



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

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

 laminae is composed of long riband-shaped fibres. These lens-jihres when 

 examined microscopically are seen to have finely serrated edges by 

 which adjacent fibres are interlocked. 



The foetal lens is nearly spherical, it is of a reddish colour, and not 

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

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

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



The Vitreous Humour occupies four-fifths of the interior of the eye- 

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

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

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

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

 by joining the capsule behind the lens. . 



Striicttire. — The vitreous humour is composed of branched connective- 

 tissue corpuscles in a jelly-like matrix. 



