350 



MANUAL OF HISTOLOGY. 



The lens (Fig. 158) is a transparent, biconvex body, sur- 

 rounded by a structureless, elastic capsule, which is thicker in 

 front where it touches the iris, and thinner behind where it 

 rests in the fossa pateUaris of the vitreous. 



The inner surface of the anterior capsule is covered with a 

 single layer of hexagonal epithelial cells, which become longer 

 near the equator of the lens, and gradually pass over into the 

 lens-fibre. 



After birth these fibres consist of long, transparent tubes, on 

 section resembling flattened hexagons closely joined together 



by their serrated edges; they are 

 arranged in concentric meridional 

 layers with their broad side out- 

 ward. They do not pass around 

 the entire circumference of the lens, 

 but arise on the anterior surface 

 from three lines, which, uniting at 

 the axis, make a figure like an in- 

 verted Y, with the arms set at an 

 angle of about 20 to each other ; 

 on the posterior surface this star 

 is reversed, the Y standing upright. 

 In adult life the rays are more 

 numerous, and the fluid contents 

 of the tubes become more solid and 

 of greater refractive power, espe- 

 cially toward the centre of the lens. 

 On a meridional section of the 

 lens one sees the concentric ar- 

 rangement of the lens-fibres, and near the equator a collection 

 of nuclei (the nuclear zone}. These nuclei belong to the lens- 

 fibres, each one of which originally had one, although in 

 adult life they are found more abundantly in the peripheral 

 region. 



The fibres of the supporting ligament of the lens (the zonula 

 ciliaris) are attached to the anterior and posterior capsule near 

 the equator ; from here they converge to the apex of the ciliary 

 body, to which they are fastened. 



The fibres form for the most part an anterior and posterior 

 layer, and have occasional nuclei, especially toward the ora 

 serrata ; between these layers is the canal of Petit, the result 



Pio. 158. Meridional section through 

 axis of the human lens. 



