224 
POPULAR SCIENCE REVIEW. 
retina, Plate XI., fig. 3), called the hyaloid membrane ( hyalos , 
crystal) ; when this membrane reaches the ciliary processes of 
the choroid (at h, fig. 3), it forms a number of plaits, similar 
in number, disposition, and size to those of the ciliary processes, 
and which are received into the folds of those processes. This 
plaited part of the hyaloid is called the zonula ciliaris ( zonula , 
a little girdle) . If, in Plate XI., fig. 3, we trace the hyaloid mem- 
brane to its termination, we see that it ends on the front sur- 
face of the lens, i, and immediately behind it, at this point, is a 
space, Jc, called the canal of Petit : this little cavity has an 
important function, and is bounded behind by the vitreous 
body, in front by the hyaloid membrane, and internally by 
the lens. 
The crystalline lens (Plate XI., fig. 3, and fig. 14) is when 
seen from the front circular, when from the side doubly convex, 
in form ; the posterior curve being the more convex of the 
two. The lens is surrounded by a membrane or capsule, that 
invests it completely ; the capsule is of the same structure as the 
elastic lamina of the cornea. The front part of the capsule is 
three or four times thicker than the part behind; which latter 
part is adherent to the tissue of the vitreous body, and there- 
fore is better supported than the capsule in front, which is 
in contact with a thin fluid, presently to be noticed. 
The lens itself is of considerable consistence, such as the 
white of an egg when gently boiled ; its density in the centre 
being greater than that of the outer part. Looking* at it in 
front, we see, when the lens is beginning to lose its transpa- 
rency, three fines, which commence at the centre and radiate 
outwards, dividing the lens into three equal parts ; the same is 
observable on the posterior surface, but the lines behind are 
placed intermediately with respect to those in front. By 
hardening it in spirit we 
rz may separate the surfaces 
j i of the lens into three parts, 
i | and we then see that it is 
j 1 composed of layers or la- 
id melke (fig. 15); and these 
FlG ‘ l6 ' again consist of fibres, which, 
in the ox, have finely -jagged 
edges (fig. 16).* Notwithstanding all this complicated struc- 
ture, the lens is perfectly transparent. 
The parts remaining to be noticed are the anterior and 
posterior chambers of the aqueous humour, the iris and the 
ciliary muscles. 
The anterior chamber ( d , Plate XI., fig. 3) is bounded, in 
Fig. 14. Fig. 15. 
* From Todd & Bowman. 
