VISUAL ORGAN. 



It consists of four layers: the anterior epithelium, the stroma 

 iridis, the posterior limiting layer, and the pigment layer. 



1. The anterior epithelium is made up of a simple layer of 

 flat cells, which cover the anterior surface of the iris. In old 

 individuals this layer is no longer to be made out. 



2. The stroma iridis consists, in Us anterior half, of reticular 

 connective tissue (anterior limiting layer), and in its posterior 

 half of loose connective tissue which contains numerous blood- 

 vessels (vascular layer). The vessels, which here have a radial 

 arrangement, possess no muscular sheaths, but are enclosed by 

 a strongly developed adventitia. In this part of the iris the 

 smooth muscle cells are collected to form the musculus sphincter 

 pupillce and the musculus dilatator pupillce. The first is formed 

 of bundles of fibres, which are arranged circularly around the 

 pupillary edge of the iris in the form of bands about 1 mm. 

 broad. The second muscle is made up of bundles of fibres 

 running radially. The pigment which is present in the con- 

 nective tissue of the iris stroma in varying quantity lends color 

 to the iris. In light eyes it is not abundant. 



The posterior limiting layer (Bruch's membrane), which is 

 a process of the lamina basalis, is a refractive membrane 2 p 

 thick. 



4. The pigment layer of the iris (pars iridica retinae) pre- 

 sents two layers of cells. The cells of the posterior layer are 

 cubical and strongly pigmented, while those of the anterior 

 layer are flat and contain only a little pigment. 



Special note must be made of those places where the cornea 

 passes over into the sclera, and where the iris and corpus 

 ciliare are connected with the outer coats of the eye. The 

 sclera passes directly over into the cornea, its fibril bundles 

 running without interruption from one coat to the other. The 

 hardly noticeable line of separation passes obliquely backward 

 and inward. In this region the ciliary border of the iris is 



o / 



attached to the outer coats of the eye. This attachment takes 

 place by means of the so-called ligamentum pectinatum iridis, 

 which in man is developed much less strongly than in many 

 lower animals. The ligament is made up of a network of fibres 



