578 TEXT-BOOK OF EMBRYOLOGY. 



eral fibers elongate more rapidly than the central, with the result that in the fully 

 developed lens the central fibers are the shortest, forming a sort of core around 

 which the now longer peripheral fibers extend in much the same manner as the 

 layers of an onion (Fig'. 505) . The ends of the fibers meet on the anterior and 

 posterior surfaces of the lens, along more or less definite lines which can be seen 













Li -■-•'' '-'•.-■• \_- fj •"■".'''." '-- .-, . '''■'■ 



tin ■■ ■ . 





:■>>> 



1 



% 





/; 



Fig. 503.— Successive stages in the development of the lens in the rabbit embryo. RaU. 



a, b, c, d, and e, are from embryos of from uj to 12 days; f, at end of 12th day; g, during the i,th 



day; h, between the 13th and 14th days; i, from an embryo of n mm. 



on surface examination and which are known as sutural lines. The lens fibers 

 are at first all nucleated and as the nuclei are situated at approximately the same 

 level m all the fibers, there results a so-called nuclear zone (Fig. 503, i) . Later 

 the nuclei disappear. The sutural lines become evident about the fifth month 

 and mark the completion of the lens formation, although lens fibers continue 

 to be formed throughout foetal and in postnatal life, probably by proliferation 



