THE EYE. 367 



branches, in part immediately enter the iris, between the 

 ciliary processes, and in part, after supplying the ciliary pro- 

 cesses, form small trunks at their border and anterior ex- 

 tremity, which are also continued upon the iris. The long 

 ciliary arteries, two in number, perforate the sclerotic on the 

 right and left a little anterior to the short ciliary vessels, run 

 in the external pigment layer of the choroid, as far as the 

 tensor chorioidece, where, each dividing into two branches and 

 joining the ciliares anticce, which to the number of five or six 

 penetrate the sclerotic in front, they constitute a superficial 

 irregular arterial circle in that muscle — the cir cuius art. iridis 

 major. From this circle, together with small vessels passing 

 either from it or from the vessels forming it to the tensor 

 muscle, very many convoluted branches, continued to the 

 iris, are given off; which, with the arteries already mentioned 

 from the choroid, divide, partly into a few true capillaries, a 

 layer of which is found particularly at the posterior surface of 

 the pupillary margin, beneath the pigment (Arnold), and 

 partly run, continually dividing, as far as the pupillary margin, 

 where, forming arched loops, they pass into fine, but still not 

 capillary, venous trunks, after they have constituted a second, 

 usually irregular circulus arteriosus minor close to the annulus 

 iridis minor. The veins of the iris arise from the arteries and 

 capillaries just mentioned, run, except frequent transverse 

 anastomosing branches, also in a radiating manner, and open : 

 1. more from the posterior surface of the iris into the vasa 

 vorticosa; 2. into the vence ciliares postica long®; and 3. 

 according to Arnold and Retzius, also into the "canal of 

 Schlemm," a narrow annular channel situated between the 

 choroid and sclerotic (fig. 295 h), from which the venule ciliares 

 anticae, passing through the sclerotic, afterwards convey the 

 blood outwardly. 



The nerves of the tunica vasculosa are also very numerous, 

 but destined solely for the ciliary muscle and the iris. They 

 are the nervuli ciliares, which perforate the sclerotic pos- 

 teriorly, then run forwards in the outer lamella of the 

 choroid, partly in grooves in the sclerotic, and, before entering 

 the ciliary muscle, divide with repeated bifurcations. Within 

 the muscle they break up into a rich and close plexus, nume- 

 rous filaments from which proceed to the muscle and to 



