VEINS OF THE CHOROID. 327 



rather tortuous trunklets, which divide dichotomously in the 

 substance of the iris. Their walls are thick in proportion to 

 their calibre. Their ramifications appear upon the anterior 

 surface of the iris as radially running vessels, anastomosing in 

 a plexiform manner, and of the same colour as the iris itself, 

 except in Albinos, in whom the colour of the blood shines 

 through the walls. Not far from the pupillary margin the 

 arteries form a circle of anastomoses, the so-called circulus 

 iridis minor. 



The capillary plexus of the iris has much wider meshes 

 than that of the choroid ; at the pupillary margin the finest 

 arterial twigs bend round in loops to become continuous with 

 the commencement of the veins. The sphincter pupillse is 

 traversed by a peculiarly fine capillary plexus. 



(3.) VEINS OF THE CHOROID. 



The vence vorticosce (h), numbering as a rule from four to six 

 large, with frequently a variable number of small vessels (in 

 some instances amounting to as many as ten), are characterized 

 by the whorl-like arrangement of their branches, which radiate 

 outwards in all directions. The smaller vessels form incomplete 

 vortices ; receiving vessels from certain directions only. The 

 larger ones, on the other hand, collect their branches from every 

 side, and receive the blood from the choroid proper, the ciliary 

 body, and the iris. Their ramifications form very numerous 

 anastomoses, which, lying on a superficial plane, decussate, for 

 the most part at very acute angles, with the straighter ciliary 

 arteries. Between each two adjoining whorls, loop-like anas- 

 tomoses wander over the posterior segment of the choroid, 

 which sometimes also receives a number of straighter branches 

 from the fore part. The veins of the iris, of the ciliary pro- 

 cesses, and a portion of the veins of the ciliary muscle, form 

 numerous parallel and frequently anastomosing vessels of 

 nearly equal size, which run backwards through the orbiculus 

 ciliaris (pars non-plicata) to the choroid. In the region of the 

 ciliary body they all lie upon the inner surface of the mem- 

 brane, but pass to the outer surface of the choroid at the 

 ora serrata. They gradually unite to form larger vessels, and 

 having reached the choroid, receive branches from that mem- 



