

HISTOLOGY OF THE LENS. 367 



As a general rule, the superficial fibres of the lens are 

 broader and thicker than those more deeply placed. Moreover 

 the area of the transverse section of the fibres is not the same 

 throughout their whole length. In Man the fibres which are 

 situated at the border of the lens, and, as above mentioned, are 

 curved outwards, are thicker at their extremities than at their 

 centre. Those fibres, on the other hand, which lie nearer to 

 the nucleus, and whose ends are curved towards the axis of the 

 lens, become gradually more and more attenuated from their 

 centre or ^equatorial portion towards the two extremities, 

 though they slightly expand again at their apices. The greater 

 number of the fibres of the lens in Mammals terminate at some 

 point of the surface with thickened or expanded extremities. 

 If the fibres of the lens reach to the axis (as from what has 

 been stated above is seen to occur in some Fishes, Amphibia, 

 . and Birds), or if they meet in one line only (as in the Rab- 

 bit, Hare, etc.), it is self-evident that they cannot expand, 

 but must gradually become narrower from the sequatorial 

 region, to terminate either, as in the former cases, in a very 

 pointed extremity, or, as in the latter, by a more or less blunt 

 point. 



The contour line of the fibres also varies. In all animals the 

 superficial ones have always smooth, the deeper, on the other 

 hand, uneven or dentated edges. This is the case in Man, 

 especially at the extremity of the fibres. The dentation is 

 more marked in Mammals, and still more in Amphibia and 

 Birds. In the greater number of Fishes, as Brewster long ago 

 pointed out, the fibres are beset with long and regularly 

 disposed dentations (fig. 376), 



However long the teeth may be, they diminish regularly in 

 size towards the extremities of the fibres, and ultimately form 

 mere wavy elevations. The teeth of one fibre are directed 

 towards those of another, with which they probably inter- 

 lock. In Mammals and Birds, however, this certainly does not 

 occur. 



Those fibres which are more or less deeply situated near the 

 border of the lens, all possess a single sharply defined oval 

 nucleus, in the centre of which is a round nucleolus. The 

 position of the nucleus varies in different fibres. In closely 



