414 



THE SKIN AXD THR SEXSE-ORGANS. 



Fig. 257. 



Lvoad and thicker, those towards the border are narrower. These 

 cells are striated, both longitudinally and transversely (Arnold). 

 The cells near the margin, however, have no transverse striation 

 (Hoffmann). The cells of the central parts form a much closer and 

 firmer structure than those at the periphery (Arnold). The peri- 

 phei'al cells are nucleated, and sometimes even possess two nuclei to 

 one cell ; the central cells have no nuclei (Arnold). 



The cells are held together by a cement-substance and by theii' 

 serrated surfaces ; the serrations are the cause of the transverse 

 striations. The fibres of the lens have a simple arrangement : com- 

 mencing at the middle point or pole of one surface they pass over 

 the equator to the opposite pole ; consequently the long borders of 

 adjacent cells are in ju^xtaposition, and their pointed extremities 

 meet at points in the axis of the lens (Hoffmann). 



Ritter has described short, nucleated cells in the centre of the 

 lens ; these are held by Babuchin to be cells which have been 

 arrested in their development. 



e. The retina is the innermost coat 

 of the eye; in the recent state it is 

 pale, soft, and smooth. The structures 

 composing it are arranged in ten 

 layers ; from the deeper surface 

 towards the choroid these are : the 

 internal limiting membrane, the 

 optic-fibre layer, the gang-lion layer, 

 the inner molecular layer, the inner 

 nuclear layer, the outer molecular 

 layer, the outer nuclear layer, the 

 external limiting membrane, the layer 

 of rods and cones, and the pigment 

 layer. 



These layers are held together by connective-tissue elements, 

 (i) The internal limiting membrane [J\rembrana fini if ans in- 

 ferva) will be descril>ed together with the connective-tissue ele- 

 ments (10). 



(2) The optic-fibre layer is formed by the fibres of the optic 

 nerve. The nerve-fibres in their course towards the eye are 

 possessed of medullary sheaths, but on piercing the sclerotic these 

 sheaths are lost. The fibres are now pale, non-medullated, and of 

 very varying thickness. In the mass of filjres nothing can be seen 

 except an extremely fine fibrillation and very fine varicosities ; the 



-AiTiT/\ivj^TjyV~N-'^~^'^ 



Fibres from tlie lens of the frog ; after 

 Hofllinann. Magnifieil 700 times. 



