802 



DISSECTION OF THE EYE. 



lines on the 

 surfaces ; 



and fibrous. 



Change in 

 form of lens, 



in colour 

 and con- 

 sistence, 

 with age. 



from the circumference to the centre ; for while the superficial 

 layers may be rubbed oft' with the finger, the deeper portion is firm, 

 and is named the nucleus. 



On each surface are three lines diverging from the centre, and 

 reaching towards the margin ; they are the edges of planes or 

 " septa," where the ends of the lens-fibres meet, and are so situate 

 that those on one side are intermediate 

 in position to those on the other. In 

 the human eye they are not distinctly 

 seen, because they bifurcate repeatedly 

 as they extend outwards. 



Structure. After the lens has been 

 hardened by spirit or by boiling, it may 

 be demonstrated to consist of a series 

 of layers (fig. 294) arranged one within 

 another, like those of an onion. The 

 laminae of each surface have their apices 

 in the centre, where the septa meet ; 

 they may be detached from one another 

 at that spot, and turned outwards to- 

 wards the equator of the lens. The 

 laminae are composed of fine parallel 

 fibres which run between two septa 

 on opposite aspects of the lens. 



Changes in the lens with age. The form of the lens is nearly 

 spherical in the foetus ; but its convexity decreases with age, 

 particularly on the anterior surface, until it becomes flattened in 

 the adult. 



In the foetus it is soft, rather reddish in colour, and not quite 

 transparent ; in mature age it is firm and clear ; and in old age it 

 becomes flatter on both surfaces, denser, and of a yellowish colour. 



FIG. 294. A REPRESENTA- 

 TION OP THE LAMINA IN A 

 HARDENED LENS. 



a. The nucleus. 



b. Superficial laminae. 



