302 



ELEMENTS OF HISTOLOGY. [Chap, xxxvn. 



-f 



iris : these are the bundles of the dilatator pupillce, 

 forming a sort of thin membrane near the posterior 

 surface of the iris (Henle and others). At the ciliary 

 margin the bundles take a 

 circular direction, and form a 

 plexus (Ivaiioff). 



422. The blood-vessels 

 (Fig. 153) of the iris are 

 very numerous. The arteries 

 are derived from the circulus 

 arteriosus iridis major, situated 

 at the ciliary margin of the 

 iris, and from the arteries of 

 the ciliary processes. These 

 arteries run in a radiating 

 direction towards the pupillary 

 margin, where they terminate 

 in a dense network of capillaries 

 for the sphincter pupillse. But 

 there are also numerous capil- 

 lary blood-vessels of a moie or 

 less longitudinal direction near 

 the posterior surface of the iris. 

 The veins accompany the arte- 

 ries, and both are situated in 

 the middle stratum of the 

 substantia propria. 



In the sheath of the blood- 

 vessels are lymph clefts and 

 lymph sinuses ; there appear to 

 be no other lymphatics. 



423. The nerve -fibres 

 are very numerous (Arnold, 

 Formad), and in the outer or 



ciliary portion of the iris form a rich plexus, from 

 which are derived, (a) networks of non-medullated 

 fibres for the dilator pupillse; (b) a network of fine 



Fig. 153. Blood-vessels 

 (injected) of the Iris 

 and Choroid Membrane 

 of the Eye of a Child. 



a. Capillaries of the choroid ; 

 6, ora serrnta ; c, blood- 

 vessels derived from d, 

 those of the ciliary pro- 

 cesses, and from e, those 

 of the iris ; /, capillary net- 

 work of the pupillary bor- 

 der. (.Kb'lliker, after Arnoid.\ 



