456 



THE EYE. 



also supply the ciliary muscle, the ciliary processes, and the iris, and 

 anastomose in the ciliary ring with the branches of the short pos- 

 terior and anterior ciliary arteries. The latter lie beside and partly 

 within the straight ocular muscles, penetrating the latter at the an- 

 terior margin of the sclera ; they give off branches to the circulus 

 arteriosus iridis major and to the ciliary muscles, anastomosing at 

 the same time with the posterior ciliary arteries. (Compare Figs. 

 352 and 357.) Within the iris the blood-vessels generally take 

 a radial direction, but also anastomose with one another, forming 

 capillaries, and subsequently the circulus arteriosus iridis minor at 

 the inner pupillary margin. From the region supplied by the 

 posterior ciliary arteries most of the blood is carried toward the 

 vorticose veins. The anterior ciliary veins convey the blood com- 

 ing from the arteries of the same name. Into these veins is also 

 poured the blood from the veins lying in the canal of Schlemm, 

 the canal itself being in reality an open venous sinus. Besides this, 

 these veins convey also venous blood from the conjunctiva (Leber). 

 1 The nonstriated muscle of the ciliary body and iris receives its 

 innervation through sympathetic nerve-fibers, neuraxes of sympa- 

 thetic neurones, the cell- bodies of which are situated either in the 

 ciliary ganglia or in the superior cervical ganglia. The neuraxes 

 of the sympathetic cells forming the ciliary ganglia form the short 



ciliary nerves, which pierce 

 the sclera in the neighbor- 

 hood of the optic nerve and 

 pass forward, to terminate in 

 the muscle of the ciliary body 

 and the sphincter muscle of 

 the pupil. Stimulation of 

 these nerves causes a con- 

 traction of the ciliary muscle 

 and a closure of the pupil. 

 The cell-bodies of the sympa- 

 thetic neurones forming the 

 ciliary ganglia are surrounded 

 by pericellular plexuses, the 

 terminations of small medul- 

 lated nerve-fibers (white rami 

 fibers) which reach the ciliary 

 ganglia through the oculo- 

 motor nerves. Neuraxes of 

 sympathetic neurones, the 

 cell-bodies of which are sit- 

 uated in the superior cervical 

 ganglia, reach the eye through 

 the cavernous plexuses, to ter- 

 minate, it is thought, in part, 

 at least, in the dilator of the 

 iris, since stimulation of these nerves causes a dilatation of the 



Margin of 

 pupil. 



Choroid. 



Fig. 357. Injected blood- vessels of the human 

 choroid and iris ; X 7- 



