RETINA 579 



and ar^ distributed in the chorioid coat between the vasa 

 vorticosa and the membrana chorio-capillaris. 



The long posterior ciliary arteries, also branches of the 

 ophthalmic, are only two in number. They perforate the 

 sclera on either side of the optic nerve (Fig. 252), a short 

 distance beyond the short ciliary arteries, and then pass 

 anteriorly between the sclera and the chorioid. When 

 they gain the ciliary zone each artery divides into an 

 ascending and a descending branch, and these, with the 

 anterior ciliary arteries, form an arterial ring termed the 

 rirculus iridis major. Branches are given off from this circle 

 to the ciliary muscle, the ciliary processes, and the iris. 



The circulus iridis minor is the name applied to a second arterial ring 

 in the iris at the outer border of the sphincter pupillge. 



The anterior ciliary arteries are very small twigs, which 

 arise from the branches of supply to the recti muscles. 

 They pierce the sclera close to the margin of the cornea, 

 take part in the formation of the circulus iridis major, and 

 send twigs to the ciliary processes. 



Venae Vorticosae. From each venous vortex in the 

 chorioid a large vein arises, which makes its exit from .the 

 eyeball by piercing the sclera, obliquely, a short distance 

 posterior to the equator. They are four or five in number. 



Dissection. The vitreous body and retina, in the posterior part of the 

 eyeball which was cut into two for the purpose of exposing the ciliary 

 processes from the posterior aspect, should now be dislodged. By raising 

 the chorioid coat from the deep surface of the sclera, under a flow of 

 water from the tap, the venae vorticosse entering the deep surface of the 

 sclera will be brought into view. When these are divided, and the separa- 

 tion of the two coats is carried posteriorly towards the optic entrance, the 

 posterior short ciliary arteries, as they emerge from the sclera and enter the 

 posterior part of the chorioid, will be seen. 



In the eyeball from which the sclera and cornea have been removed, 

 the iris, ciliary processes, and the chorioid should be carefully stripped -off 

 piecemeal under water. This will expose the retina. 



Retina. The retina is composed of two strata viz., a 

 thin pigmentary layer, which adheres to the deep surface of 

 the chorioid coat, and has been removed with it, and a 

 delicate nervous layer, which is moulded on the surface of 

 the vitreous body, but presents no attachment to it except at 

 the optic entrance. The retina extends anteriorly, beyond 

 the equator of the eyeball, and, a short distance from the 

 ciliary zone, it appears to end in a well-defined wavy or 



