NERVE 



141 



firmly adherent to the processes that it is difficult to strip 

 it off. It passes forward from the processes as the susj^ensory 

 ligament (8.L.), and then splits to form the lens capsule. 

 In this is held the crystalline lens (L.), a biconvex lens, 

 with its greater curvature on its posterior aspect. It is an 

 elastic structure, and it is normally kept somewhat pressed 

 out and flattened between the layers of the capsule ; but, 

 if the suspensory ligament is relaxed, 

 its natural elasticity causes it to 

 bulge forward. This happens when 

 the ciliary muscle contracts and pulls 

 forward the ciliary processes with 

 the hyaloid membrane. 



Between the hyaloid membrane 

 and the choroid is the retina (Ret.). 

 This is an expansion of the optic 

 nerve, which enters the eye to the 

 inner side of the posterior optic 

 axis (fig. 62). The white nerve 

 fibres pass through the sclerotic, 

 through the choroid, and through 

 the retina, to form the white ojJtic 

 disc. This is about lo mm. 

 in diameter in the human subject. 

 The fibres lose their white sheath, and 

 spread out in all directions over the 

 front of the retina, to form its first 

 layer — the layer of nerve fibres (1) 

 (fig. 63). These nerve fibres take 

 origin from a layer of nerve cells (2) 

 behind them, forming the second 

 layer. The dendrites of these cells arborise with the 

 dendrites for the next set of neurons in the third 

 layer, the internal molecular layer (8). The cells of 

 these neurons are placed in the next or fourth layer, the 

 inner nuclear layer (4), and from these cells, processes pass 

 backwards to form synapses in the fifth, or outer molecular 

 layer (5), with the dendrites of the terminal neurons. These 

 terminal neurons have their cells in the sixth or outer nuclear 



Fig. 63. ^Diagram of a Sec- 

 tion through the Retina 

 stained by Golgi's method. 

 For description, see text. 

 (From Van Gehuchten.) 



