78 SEVENTH LECTURE. 



To close with the epithelial productions, we here notice 

 briefly the tissue of the crystalline lens of the eye. This 

 (Fig. 72), arising from an ingrowth of the corneal plate of the 

 foetus, is invested by a structureless capsule {a, a), which is 

 thicker anteriorly and thinner posteriorly. The inner surface 

 of the anterior segment of the capsule has an unstratified, 

 low, cubical pavement epithelium (b). 



The marginal zone of the latter, advancing towards the 

 equator, undergoes a gradual transition into elongated nuclear 

 elements, the so-called lens fibres (c). These are 

 pale, hyaline elements, in the external portion 55 

 of the organ, 0.009 to 0.0113 mm. ; in the inter- 

 nal, where they appear more firm, only 0.0056 

 mm. broad. The lens fibre, surrounded by a 

 fibres in trans- sor t f envelope, has the value of a full-grown 



verse section. * ' ° 



cell. The nuclei (f) lie adjacent to the equatorial 

 zone. The arrangement is, in general, meridional. Trans- 

 verse sections of the lens fibres present an elegant band of 

 elongated hexagons (Fig. 73). 



Fig. 73.— Lens 

 ibres in tr; 

 verse section 



