THE IRIS. 315 



decussation : a. Pale fibres, in all probability belonging to the 

 sympathetic, which run towards the posterior surface of the 

 iris (consequently to the dilatator), on which they form a very 

 fine plexus, b. Medullated fibres, which pass to the anterior 

 surface, and there break up into a close plexus of fine fibres ; 

 these are the sensory fibres of the iris. c. Lastly, a third 

 plexus is distributed within the sphincter ; its delicate nerves 

 are for the most part motor. 



The vessels, muscles, and nerves of the iris are imbedded in 

 a stroma, which is chiefly composed of connective-tissue fibrils 

 and cells. 



The connective tissue accompanies the vessels in the form of 

 thin fasciculi of fibrils ; but fibres are also met with in the 

 interspaces, most of which run in a longitudinal direction. 



In black eyes the principal portion of the stroma is composed 

 of pigmented stellate cells, which form close anastomoses with 

 each other. These cells are most closely arranged in the most 

 superficial layers of the iris. In black eyes we meet also with 

 many free, round, strongly pigmented cells. 



In light-coloured eyes, non-pigmented stellate cells, with 

 long thin processes, are met with, and, in addition, a great num- 

 ber of round cells resembling the lymph corpuscles. 



