266 



THE ESSENTIALS OF HISTOLOGY. 



ally into others which run circularly around the circumference of the 

 iris, and on a level with the ciliary processes. This set of circularly 

 arranged bundles constitutes the circular ciliary muscle of H. Muller (L) ; 

 it is most marked in hypermetropic eyes. 



The iris is that part of the vascular coat of the eye which extends in 

 front of the lens. It is continuous with the choroid and has a similar 



Outer or choroidal surface. 



8. Layer of pigment-cells. 



7. Layer of rods and cones. 



. . Membrana limitans externa. 



(5. Outer nuclear layer. 



5. Outer moleciilar layer. 



4. Inner nuclear layer. 



3. Inner molecular layer. 



2. Layer of nerve-cells. 

 1. Layer of nerve-fibres. 



. . . Membrana limitans interna. 



Inner surface. 



FIG. 297. DIAGRAMMATIC SECTION OF THE HUMAN RETINA. (M. Schultze.) 



structure, but its pigment-cells often contain variously coloured pig- 

 ment. Besides the homogeneous connective tissue with numerous 

 elastic fibres and blood-vessels of which it is chiefly composed, it con- 

 tains two sets of plain muscular fibres. The one set forms the sphincter 

 muscle (fig. 295, a), which encircles the pupil, the other set consists of 

 a flattened layer of radiating fibres which extend from the attachment 



