THE LENS AND ZONULE 19 



The Lens and Zonule — The crystalline lens is a glassy, cushion- 

 shaped body which lies behind the iris (Figs. 3 and 5). It is supported 

 from behind by the vitreous body and from the front, to some extent, 

 by the iris. The slightly conical form of the iris is entirely owed to the 

 light pressure of the lens against it. If the lens is removed, as in an oper- 

 ation for cataract, the iris thereafter hangs loosely and trembles when- 

 ever the eye moves. 



The chief support of the lens is given by a great number of firm 

 threads which, like so many guy-ropes, run from the rim of the lens to 

 the ciliary body. Collectively, these threads form the suspensory liga- 

 ment or zonule of Zinn (Fig. 3; Fig. 5, ^/). Each zonule fiber arises from 

 the surface of the ciliary epithelium, runs forward between two adjacent 

 ciliary processes, and sweeps around toward the lens equator to fuse with 

 the capsule of the lens. The largest number of fibers insert on the an- 

 terior face of the lens near the equator, a rather smaller number on the 

 posterior face, also near the equator; and scattered fibers insert at the 

 equator everywhere between these anterior and posterior sheets of fibers 

 ('anterior and posterior leaves of the zonule'). Some atypical fibers cross 

 each other between the zonule leaves, and others run from one ciliary 

 process to the next and do not join to the lens at all. A little behind 

 the posterior zonule leaf (which is bowed to fit its curvature) lies the 

 anterior membranous surface of the vitreous, which is joined to the pos- 

 terior lens capsule along a narrow ring (Egger's line; Fig. 5, el) but is 

 free of the posterior lens surface in its center, creating the fluid-filled 

 'retrolental space' (Fig. 3; Fig. 5, rs). Between the anterior hyaloid mem- 

 brane of the vitreous and the posterior leaf of the zonule is the flattened 

 annular 'canal of Petit'. Between the leaves of the zonule is the space 

 called the 'canal of Hannover' — though of course it is not a true canal 

 since the fibers in each leaf of the zonule do not form an intact mem- 

 brane, but rather a grille. Between the anterior leaf and the back of the 

 iris lies the posterior chamber sensu stricto (Fig. 5, pes), although the 

 term 'posterior chamber' is properly enough used to embrace collectively 

 all of the aqueous-filled spaces behind the iris. 



Newly-formed aqueous, poured into the posterior chamber by the 

 ciliary epithelium, can get into the anterior chamber (between iris and 

 cornea) only by infiltrating between the zonule fibers and then passing 

 between lens and iris and through the pupil. If, in an inflammation of 

 the iris, the whole pupil margin adheres to the lens capsule, the aqueous 



