64 



THE EYE. 



adult are somewhat variable and numerous on the surfaces (fig. 72), but in the foetal 

 lens throughout, and towards the centre of the lens in the adult, they are three in 

 number, diverging from each other like rays at equal angles of 120 (fig. 73). The 

 lines which converge to the opposite poles have an alternating position. Thus 

 of those seen on the posterior surface of the foetal lens, one is directed vertically 

 upwards, and the other two downwards and to either side, whereas those on the 

 anterior surface are directed one directly downwards and the other tAvo upwards and 

 to the sides. These lines are the edges of planes or septa within the lens diverging 

 from the axis, and receiving the ends of the lens-fibres, which here abut against one 



Fig, 74. LAMINATED STRUC- 

 TURE OF THE CRYSTAL- 

 LINE LENS, SHOWN AFTER, 

 HARDENING IN ALCOHOL 



(Arnold), f 

 1. nucleus ; 2, 2, lamellae. 



another. As Tweedy has 

 pointed out, they may 

 be seen, by the aid 

 of the ophthalmoscope, 



even during life. The rays seldom meet at a point, 

 but usually along a somewhat irregular area. 



Structure. When the lens has been hardened 

 and the capsule removed, a succession of concentric 

 laminae may be detached from it like the coats from 

 an onion. They are not continuous, but separate 

 into parts opposite the radiating lines above de- 

 scribed (fig. 74). The laminae are composed of 

 long, riband-shaped, microscopic fibres, 0'005mm. 

 broad, which adhere together by their edges, the 

 latter being often finely serrated (fig. 75, A). 

 The serrations of adjacent fibres abut against 

 one another so as to leave as in other epithelial 



Fig. 75. FIBRES OF THE CRYSTALLINE LENS. 350 DIAMETERS. 



A, longitudinal view of the fibres of tbe lens from the ox, 

 showing the serrated edges. B, transverse section of the fibres 

 of the lens from the human eye (from Kolliker). C, longi- 

 tudinal view of a few of the fibres from the equatorial region 

 of the human lens (from Henle). Most of the fibres in C are 

 seen edgeways, and, towards 1 , present the swellings and nuclei 

 of the "nuclear zone ;" at 2, the flattened sides of two fibres 

 are seen. 



structures fine interfibrillar or intercellular channels for the passage of fluid. 

 The lens-fibres pass in a curved direction from the intersecting planes of 

 the anterior half of the lens to those of the posterior half, or vice versa : in this 

 course no fibre passes from one pole to the other, but those fibres which begin near 

 the pole or centre of one surface, terminate near the marginal part of a plane on 

 the opposite surface, and conversely ; the intervening fibres passing to their corre- 

 sponding places between. The arrangement will be better understood by a reference 

 to fig. 73, where the course of the fibres in the foetal lens is diagrammatical ly 

 indicated. 



The lens-fibres, as the history of their development shows, are to be looked upon 

 as greatly elongated cells. In the young state each has a clear oval nucleus, but in 



