IX 



RODS AND CONES 



425 



e.l.m. 



Seen sideways each cell is found to be provided with 

 long, fine, hair-like processes, which stretch in towards 

 the retina and envelop the outer ends of the rods and 

 cones (Fig. 139, b.c). 



The rods and cones each consist of two parts, an outer 



limb and an inner 

 limb. In the rods the 

 outer limb is quite cylin- 

 drical or rod-shaped, and 

 is transversely striated. 

 The inner limb is about 

 as long as the outer, but 

 bulges out slightly in its 

 middle part, so that it 

 forms an elongated cylin- 

 der tapering at each end. 

 The outer part of each 

 inner limb is longitudi- 

 nally striated. The inner 

 end of each inner limb 

 is prolonged into a fine 

 filament, which carries a 

 conspicuous nucleus, often 

 marked transverselj', and 

 may be easily traced into 

 the outer molecular layer 

 (Fig. 140, R.). 



The outer limb of a 

 cone is much shorter than 

 the outer limb of a rod, 

 and instead of being rod- 

 shaped, is conical and 

 tapering to its outer point ; this outer limb is 

 transversely striated. The inner limb of each cone is 

 thicker than the inner limb of a rod, but of the same 

 general shape. It is striated" longitudinally in its outer 

 part and carries a large nucleus from which a thick fibre 



o.m.l 



R. C 



FlQ. 



140. — Diagram of 



OF A CONF.. 



Rod and 



R, rod ; C, cone ; o, outer limb ; ;', 

 inner limb ; e.l.m, external limiting 

 membrane of retina ; o ni.l, outer 

 molecular layer of retina. 



