700 HANDBOOK OF PHYSIOLOGY. 



The lens itself is made up of transparent longitudinal fibres, hexag- 

 onal and prismatic, thickened posteriorly. Those fibres at the cortex 

 have nuclei and are smooth, those near the centre are without nuclei 

 and have serrated edges. The fibres are united together by a scanty 

 amount of cement substance. 



The arrangement is such that no fibres run the whole half of the 

 lens, from front to back, since, if a fibre starts near the anterior pole, 

 its other end is far from the posterior pole (fig. 415.) 



The epithelium of the lens consists of a layer of cubical cells anteriorly, 

 which merges at the equator into the lens fibres. The development of 

 the lens explains this transition. The lens at first consists of a closed 

 sac composed of a single layer of epithelium. The cells of the posterior 

 part soon elongate forward and obliterate the cavity, the anterior cells do 



Fig. 415. Meridional section through the lens of a rabbit. 1, Lens capsule- 2, epithelium of 

 lens; 3, transition of the epithelium into the fibres; 4, lens fibres. (Bubuchin.) 



not grow, but at the edge they become continuous with the posterior 

 cells, which are gradually developed into fibres. The lens contains 

 globulin or crystallin, but no native-albumin; it also contains choles- 

 terin. The capsule is a homogeneous transparent elastic membrane. 

 The hardest portion of the lens is that which is most internal. It forms 

 the so-called nucleus of the lens (fig. 414, 1). 



Corneo-scleral junction. At this junction the relation of parts (fig. 

 412) is so important as to need a short description. In the neighbor- 

 hood, the iris and ciliary processes join with the cornea. The proper 

 substance of the cornea and the posterior elastic lamina become continuous 

 with the iris, at the angle of the iris, and the iris sends forward processes 

 toward the posterior elastic lamina, forming the ligamentum pectinatum 

 iridis, and these join with fibres of the elastic lamina. The endothelial 

 covering of the posterior surface of the cornea is, as we have seen, con- 

 tinuous over the front of the iris. At the iridic angle, the compact 

 inner substance of the cornea is looser, and between the bundles are 

 lymph spaces filled with fluid, called the spaces of Fontana. - They are 

 little developed in the human cornea. Where the cornea and sclerotic 

 join, there is an intermediate part which resembles both, but which is 

 still not transparent, as the internal part remains scleral in structure. 



The spaces which are present in the broken up bundles of corneal 

 tissue at the angle of the iris, are continuous with the larger lymphatic 



