ORGANS OF THE SENSES. 521 



In the Mammalia in general there are visible on the front 

 surface of the lens, when this has slightly lost its trans- 

 parency, three radiating grooves or lines, the points of which 

 terminate at about one-third from the border of the lens. 

 On the opposite surface of the lens there exist three similar 

 lines, occupying an intermediate position. From these lines 

 the fibres pass from the one surface on to the other ; thus a 

 fibre which starts from the point of one of the lines in front, 

 passes over the border of the lens, advances midway between 

 two lines on the opposite surface, and is inserted in the 

 angle of division of those lines ; another fibre starting from 

 between two lines in front, is lost on the extremity of a line 

 situated posteriorly : the rest of the fibres occupy positions 

 intermediate to these. If, in the next place, we bear in 

 mind the fact that these lines, seen on the surface of the 

 lens, are but the edges of planes which pass through the 

 centre of the lens, affording points of divergence and con- 

 course for all the fibres, deep as well as superficial, we shall 

 readily comprehend what, without this explanation, would 

 have appeared an intricate arrangement ; and we shall per- 

 ceive why it is that the lens, when hardened in spirit or 

 boiled in water, is prone to separate into concentric lamella 

 and into three triangular segments. From the above ar- 

 rangement it results, also, that all the fibres, whether super- 

 ficial or deep-seated, decrease in width as they approach the 

 centre of the lens on either surface, and also that the super- 

 ficial are longer and larger than the deeper seated. (See 

 Plate LX VII. fig. 13.) 



The edges of the fibres are most beautifully toothed and 

 dovetailed together, as was first pointed out by Sir David 

 Brewster. This toothing is best seen in the eyes of fishes ; 

 it is also clearly manifest, although on a smaller scale, in the 

 fibres of the lens of most mammalia and of man. (See 

 Plate LXVIL^. 10.) 



On the surface of the lens beneath the capsule, and occu- 

 pying the space between these, a delicate epithelium exists, 

 very similar to that on the posterior elastic lamina. (See 



