852 



OBGANS OF SPECIAL SEXSE 



The vena centralis retinae returns the blood of the corresponding artery, 



2. The ciliary system of blood-vessels (pafi;es500, 501, and ()25j. — There are 



three sets of arteries belonging to this s}'steni, all derived directly or indirectly 



from the ophthalmic artery. 



(1) Short posterior ciliary arteries, twelve to twenty in number, pierce the 

 sclerotic round tlie optic nerve entrance, and are distributed in tlie choroid. 

 Before entering the eyeball, small twigs are given off to the adjoining sclerotic and 

 to the dural sheath of the optic nerve. 



(2) Two long posterior ciliary arteries, piercing the sclerotic further from the 

 nerve than the short ciliaries, run horizontally forwards between the sclerotic and 

 choroid, one on each side of the globe. On arriving at the ciliary body, they 

 join with the anterior ciliary arteries, forming the circulus iridis major, which 

 sends off branches to tlie ciliary processes and the iris. The long ciliaries also 

 give twigs to the ciliary muscle, and small recurrent branches run backwards to 

 anastomose Avith the short ciliary arteries. The arteries of the iris run radially to 

 the })upillary ]»order, anastomosing with one another oj^posite the outer border of 

 the sphincter so as to form the circulus iridis minor. 



(3) The anterior ciliary arteries come from the arteries of the four recti 



Fig. 479. — Surface of Choroid and Iris exposed by removal of Sclerotic and 

 Cornea, showing Distribution of Blood-vessels and Nerves. 



(Twice natural size. After Zinn.) 



A CILIARY NERVh 



SURFACE OF CHOROID IN 

 CILIARY REGION 



A CILIARY NERVE 



Long posterior ciliary 

 artery 



FLAP OF SCLEROTIC, 

 REFLECTED 



muscles, one or two from each; they run forwards, branching as they go, and 

 finally pierce the sclerotic near the corneal border. Outside the globe they send 

 twigs to the adjoining sclerotic, to the conjunctiva, and to the border of the cornea. 

 After passing through the sclerotic the arteries enter the ciliary muscle, where they 

 end in twigs to the muscle and to the circulus iridis major, and recurrent branches 

 to the choroid. 



Veins. — The venous blood from almost the whole uveal tract (choroid, ciliary 

 processes and iris, and part of the ciliary muscle) ultimately leaves the eyeliall by 

 (1) the venae vorticosae, which have been already noticed in describing an antero- 

 posterior section through the globe. One large vein passes backwards from each 

 vortex, piercing the sclerotic obliquely; it is joined by small ei)iscleral veins when 

 outside the glol)e. 



(2) The anterior ciliary veins commence by the junction of a few small veins 

 of tiie ciliary muscle; they pass outwards through the sclerotic near the corneal 

 border, receiving blood from the veins in connection with Schlemm's canal, and 

 afterwards from episcleral and conjunctival veins, and from the marginal corneal 

 plexus. Finally tliey join the veins running in the recti muscles. 



Lymphatic system of the eyeball. — A])art from those in the conjunctiva 



