io8 



HUMAN PHYSIOLOGY 



humour. The vitreous humour is enclosed in a delicate 

 fibrous capsule, the hyaloid membrane, and just behind the 

 ciliary processes this membrane becomes tougher, and is 

 so firmly adherent to the processes that it is difficult to strip 

 it off. It passes forward from the processes as the suspensory 

 ligament (S.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 pos- 

 terior aspect, and characterised by 

 its great elasticity. Normally it 

 is kept somewhat pressed out and 

 flattened between the layers ot' 

 the capsule, but if the suspensory 

 ligament is relaxed its natural 

 elasticity causes it to bulge for- 

 ward. 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 at 3 to 

 4 mm. to the inner side of the 

 posterior optic axis (Fig. 45). The 

 white nerve fibres pass through 

 the sclerotic, through the choroid, 

 and through the retina, to form the 

 white optic disc, and then losing 

 their white sheath, they spread 

 out in all directions over the front 

 of the retina, to form its first layer 



the layer of nerve fibres (1). 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 (3). 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 



FIG. 45. Diagram of a Sec- 

 tion through the Retina 

 stained by Golgi's me- 

 thod. For description, 

 see text. (From VAN 

 GBHUCHTEN. ) 



