THE SENSE OF SIGHT 401 



The Vitreous Humor. It is a transparent, gelatinous 

 fluid enclosed in a transparent membrane, the hyaloid, 

 and fills about four-fifths of the eye-ball. In front 

 it is hollowed out to receive the lens and its capsule, 

 being adherent to the back of the latter. (See Fig. 

 141, page 402.) 



The Crystalline Lens. This is a solid, transparent, 

 biconvex body which lies, enclosed in its capsule, in 

 front of the vitreous and behind the iris. The greater 

 convexity is behind. 



The capsule is an elastic, transparent, structureless 

 membrane, in contact anteriorly with the iris and 

 held in place by the suspensory ligament. 



The suspensory ligament is a thin, transparent 

 membrane placed between the vitreous humor and 

 the ciliary processes, and presents externally a number 

 of folds which receive those of the ciliary processes. 



The Aqueous Humor. This is the fluid which fills 

 the space between the suspensory ligament and cap- 

 sule behind and the cornea in front. That part of this 

 space which lies in front of the iris is called the anterior 

 chamber; the part behind the iris is the posterior 

 chamber. The latter is really only the small interval 

 between the iris, suspensory ligament, and ciliary 

 processes. 



The ciliary processes, seventy or more in number, 

 consist of a circle of folds or thickenings of the choroid 

 received into pits in the vitreous and suspensory 

 ligament of the lens. They are divided into a larger 

 and a smaller set, the former being about one-tenth 

 inch in length. Their inner surface is covered by the 

 layer of hexagonal, pigmented cells in the retina. 



The Retina. This is a delicate nervous membrane on 

 which the image of perceived objects is formed. It lies 

 between the choroid and the hyaloid membrane of the 

 vitreous humor, and is composed of ten layers of cells. 

 Behind, the optic nerve expands into it, and in front it 



26 



