270 



THE RETINA, BY MAX SCHULTZE. 



of the pigment cells break up at their extremities again into 

 innumerable fine fibres, which are often quite colourless, and 

 present no distant resemblance to a brush of cilia. They extend 

 at least as far as the line of junction of the outer and inner 

 segments of the rods and cones, and in many animals as far as 

 to the region of the limitans externa. They closely embrace 

 the rods and cones, but soon break down after death, owing to 

 which the connection between the pigment cells and rods 

 becomes less firm, After the perfectly fresh retina has been 

 hardened in perosmic acid, the outer segments, even in Man, 

 however, usually adhere so firmly to the pigment cells, that 

 they rather separate from the internal segments, or fracture 

 through their substance, than become detached from the pig- 

 ment cells. 



The intensity of the pigment varies ; it is least in blonde 

 individuals, greatest in the negro. It is always darker behind 



Fig. 359. 



Fig. 359. Cells from the pigment layer of the retina of Man. 

 a. Seen in situ from the surface. 6. Seen in profile with the long 

 hair-like processes partly pigmented, partly free from pigment, c. A 

 cell also seen in profile, to which the outer segments of several rods 

 are still adherent. 



the macula lutea than in any other part of the retina. The 

 retina of Albinoes is almost or entirely free from pigment, and 

 it is absent in those parts of the retina of Mammals, where the 

 choroid presents a highly reflecting tapetum. The hair-like 

 ciliaform processes of the cells which invest the rods like a 

 sheath are nevertheless well developed in these colourless cells.* 

 The pigment granules themselves, which appear for the most 



* Max Schultze, Archie fur Mikroskop. Anatomic, Band ii., Taf. xiv., 

 fig. 9, b. 



