596 THE EYE 



of much softer consistency. The hardened central mass is the 

 so-called nucleus of the lens. 



The nuclei of the lens fibres remain in the neighborhood of the 

 equator, where they are first formed, and are thus contained within 

 a narrow, superficial, equatorial zone, the nuclear zone. 



Each lens fibre is disposed along a meridian of the lens, and 

 extends from its anterior to its posterior hemisphere ; the fibres 

 are so arranged that they abut upon one another, end to end, along 

 Y-shaped lines which radiate from either pole. This union is often 

 quite firm, and thus are formed long fibrous bands which can be 

 traced from the anterior to the posterior hemispheres of the lens. 

 These bands are distributed in a peculiar manner. Near each pole 

 along the line of abutment, the band may be said to bend upon 

 itself with a sharp curve making an angle of about 60 whose 

 convexity is directed toward the pole, the parallel fibres being so 

 arranged as to form a sector whose apex is also directed toward the 

 pole. The corresponding sectors of opposite poles overlap one an- 

 other so that the fibrous bands are continued from one side of one 

 polar mass to the reverse side of the overlapping sector and so back, 

 on the farther side, to the adjacent sector of the former hemisphere. 

 By teasing, fibrous bands can sometimes be traced successively 

 through all of the polar sectors and thus back to a sector beneath 

 that from which the start was made. Obviously no individual lens 

 fibre is of sufficient length to extend from pole to pole of the lens. 



THE VITREOUS HUMOR. The vitreous humor (vitreous 

 body) is a soft jelly-like mass which fills the entire cavity of the eye 

 behind the line of the ora serrata and crystalline lens. It is com- 

 pletely invested by the hyaloid membrane. The vitreous humor 

 appears to be a peculiarly delicate form of very loose gelatinous 

 connective tissue whose scanty fibres present a somewhat concen- 

 trically lamellated arrangement and are so very delicate as to be rec- 

 ognized under ordinary conditions only with the greatest difficulty. 



Occasionally stellate and fusiform cells, remarkable for their 

 large vacuoles and varicose processes, have been demonstrated in 

 small numbers within the vitreous, body. Small rounded cells some- 

 what resembling leucocytes are also found, but for the most part 

 they are flattened against the hyaloid membrane ; they occur in 

 very limited numbers. 



THE HYALOID MEMBRANE. The hyaloid membrane is a 

 very thin structure which surrounds the vitreous humor and unites 

 it to the inner surface of the retina and the crystalline lens. It 



