11 



immersed in the agueous humor and its posterior face im- 

 bedded in the vitrious. 



The suspensory ligament extends from its periphery to 

 the ciliary body and thus assists in holding the lens in posi- 

 tion and establishes a union between it and the ciliary 

 muscle. The lens is enveloped by an elastic capsule very 

 like Descemet's layer of the cornea. The proper tissue of 

 the lens is arranged in concentric layers that under the mi- 

 croscope are found to be composed of fibres; the external 

 layers of the lens are almost liquid, but they gradually in- 

 crease in hardness toward the center. The lens receives 

 neither blood vessels nor nerves; it absorbs its nutriment 

 from its capsule through a delicate layer of cells on its 

 surface. 



The anterior surface of the lens is flatter or less convex 

 than its posterior surface. By the contraction of the ciliary 

 muscle the convexity of the lens is changed and the degree 

 of refraction varies; thus the eye is adjusted for, or made to 

 accommodate itself to, different distances. The chief use of 

 the lens is to refract (change the direction of or bend) the 

 rays of light, which enter the eye. It causes the rays to 

 converge or unite or focus upon the retina. 



The vitrious humor occupies about two-thirds of the in- 

 terior of the eye — all of the cavity of the eye behind the 

 crystalline lens. It is transparent, colorless, jelly-like in 

 consistency and contains a few embryonic cells, while its 

 major part is amorphous or without distinct parts. The 

 hyaloid membrane envelopes the vitrious mass and is in 

 contact externally with the retina and the posterior convex 

 surface of the lens. This humor assists in the refraction of 

 light. If it escapes, it is not regenerated. 



The accessory organs of the eye are the Orbital Cavity, 

 the Muscles of the Eye, the Eye Lids, the Membrane Nicti- 

 tans and the Lachrymal Apparatus. 



The orbital cavity is situated at the side of the head, near 



