738 SPECIAL HISTOLOGY. 



likewise obtains some twigs from the same arteries, the blood is returned 

 principally through the vence vorticosce, which, lying upon the arteries, 

 constitute elegant vascular stars or vortices, two above and two below 

 (or it may be five or six); and also at the back of the eyeball, through 

 some minute vence ciliares posticce breves, all of which veins penetrate 

 the sclerotic in the same way as the arteries. 



The iris receives its blood in the first place from the arteries of the 

 choroid, and secondly, from the long posterior and the anterior ciliary 

 arteries. The former, with their anterior branches, in part immediately 

 enter the iris, between the ciliary processes, and in part, after supplying 

 the ciliary processes, 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 circulus 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 posticcv longce ; 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 venulce ciliares antica?, 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 ner- 

 vuli ciliares, which perforate the sclerotic posteriorly, 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 bifurca- 

 tions. Within the muscle they break up into a rich and close plexus, 

 numerous filaments from which proceed to the muscle and to the cornea, 

 while others constitute the proper nerves of the iris. The latter ac- 



