SECT. 225.] IX THE CHOROID AND IRIS. 55 1 



five and six), and form beautiful stellate figures or Whorls; it is 

 returned also in the fundus of tlic eye-ball, by some small vena 

 ciliares postica breves, and all of these veins penetrate the sclerotic 

 in the same manner as the arteries. 



The Iris receives its blood, firstly, from the arteries of the 

 choroid coat ; and, secondly, from the art. ciliares postica longa, 

 and the art. ciliares antica. The anterior branches of the former 

 vessels either pass directly into the iris, between the ciliary processes, 

 or, after supplying the ciliary processes, form small trunklets at 

 their border and anterior end, and these likewise proceed onwards 

 to the iris. The long ciliary arteries, two in number, penetrate 

 the sclerotic on the right and left, somewhat in front of the 

 shorter vessels of the same name, and run in the outer pigmentary 

 layer of the choroid, as far as to the tensor chorioida ; here each 

 divides into two branches, and unites with the art. ciliares antica? 

 (which, three to six in number, penetrate the sclerotic), producing 

 in the muscle mentioned an irregular arterial ring, the circulus 

 art. iridis major. From this circle very many radiated and tor- 

 tuous branches are given off into the iris, and small vessels arise 

 either from the circle, or from the vessels forming it, for the supply 

 of the tensor muscle. Arrived at the iris, these vessels are dis- 

 tributed along with the above-mentioned arteries from the choroid 

 coat, partly producing a small number of true capillaries, one 

 layer more especially being situated on the posterior surface of 

 the pupillary border beneath the pigment (Arnold) ; another part 

 of the vessels running (with some dividing continually) as far as 

 the border of the pupil, where they bend round and return into 

 the veins by loops of delicate but not capillary vessels, which form 

 a second circulus arteriosus minor, usually imperfect, in the 

 region of the annulus iridis minor. The veins of the iris arise 

 from the above-mentioned arteries and capillaries ; they form fre- 

 quent transverse anastomoses, but they also run chiefly in a radiating 

 manner ; they open, 1, into the vasa vorticosa, especially those 

 veins which spring from the posterior surface of the iris ; 2, into 

 the vena ciliares posticce ; and, 3, according to Arnold imdMetzius, 

 into the canal of Schlemm, a narrow circular canal situated between 

 the most anterior border of the choroid and sclerotic, from wdiich 

 the venula ciliares arise, aud conduct the blood outwards through 

 the sclerotic. 



The nerves of the tunica vasculosa are likewise very numerous, 

 but are destined exclusively for the ciliary muscle and for the iris. 

 The nervuli ciliares penetrate the sclerotic posteriorly with fifteen 



