STRUCTURE OF THE EETIXA. 



607 



hoWov^, fovea cenfraVs, and, as the retina is thinner here than elsewhere, 

 the pigmentary layer is clearly visible through it, giving rise to an appear- 

 ance as of a hole through the tunic. About yV^^^ o^' '^^i i^^ch inside the 

 yellow spot is the round disc, poms opticus, where the optic nerve ex- 

 pands, and in its centre the point from which the vessels of the retina 

 branch. At this place the nervous substance is slightly elevated so as 

 to form an eminence (collmdus ncrvi ojjfici) (fig. 418, k, k.). 



MICKOSCOPIC STRUCTURE OF THE RETINA. 



"When vertical sections of the retina, i.e., sections made perpendicularly 

 to its surface, are submitted to microscopic examination, eight distinct 

 strata are recognizable, together with certain fibrous structures which 

 pass vertically through the membrane and connect the several layers. 



Fi-. 41 D 



Outer or choroidal surface. 



'^rW''-y'^W^^c S. Layer of pigment cells. 



! I ■ : l! 1 ! I ' ; ; 





7. Laj-er of rods and cones. 



I\Icmbrana limitans externa. 





^%r 



Outer nuclear layer. 



5. Outer moleculai" layer. 



3. Inner molecular layer. 



JlDllSf " 



er of nerve cells. 



^ 1. Layer of nerve iilires. 

 ^ . . . Membrana limitans interna. 



Inner surface. 



Fio-. 419.— DiAGRAvIMATIC ShCTIOX OF THE HuMAN ReTIKA (Scliultzc). 



