412 THE SKIN AND THE SENSE-ORGANS. 



and proximal part of the upper surfaces. Towards the corpus 

 ciliare the meshes become wider and elongated ; the capillaries then 

 unite at acute angles parallel with the longitudinal axis of the 

 eye. The network {choriocapillaris) exists in a simple layer within 

 the two arteries which form it^ and superficial to the veins (Virchow). 



^. The veins of the choroid (Fig. 256 III^ IV, IX) are (i) a vein 

 which unites at the lowest point of the equator of the eye with the 

 V. hyaloidea to form (2) the V. ophthahinca, two small branches of the 

 V. hidbi superior, which unite outside the sclerotic, and (3) the vasa 

 recta. 



(i) The larger vein arises from the greater part of the under 

 surface of the eye ; it gives off branches to each side, which radiate to 

 form a ' whorl ' or star-shaped capillary anastomosis (Fig. 256 III), 

 the two halves of which have no connection. A proximal and a 

 distal root can be distinguished in the anastomosis ; the distal lies 

 towards the corpjus ciliare, and occupies exactly one-fourth of the 

 circumference of the choroid at its junction with the corpîis ciliare. 



(2) The two branches of the V. hulbi superior lie alongside the 

 corpms ciliare on the upper surface, and each occupies one-fourth 

 of the circumference ; they form a similar though simpler figure 

 (Fig. 256 I) to the foregoing, each forming one half. 



(3) The vasa recta are numerous parallel vessels which arise in the 

 iris, and coursing centrally empty themselves into the branches of 

 the V, Imlbi superior on the superior surface, and into the branches 

 of the venoiTS capillaries on the inferior surface. 



2. The iris is covered anteriorly by a layer of endothelium, 

 continuous with that covering the posterior surface of the cornea, 

 and of similar character. The border of the pupil {^iiargo piipiUaris) 

 is of a golden colour, outside this bright ring to its oviter margin 

 {rnargo ciliaris) the iris is black ; the golden colour is due to the 

 presence of cells containing a pale yellow pigment ; the nuclei of 

 these cells are round and granular; the cells themselves have 

 rounded outlines (Hoffmann). The black portion of the iris con- 

 tains more irregular, spindle-shaped cells, with round nuclei, which 

 are hidden by a dense mass of pigment-granules (Iwanoff and 

 Hoffmann). 



The true substance of the iris consists of muscle, nerves, blood- 

 vessels, and a connective-tissue stroma, but on the posterior surface 

 is another layer of black, pigmented cells, and tjiis is again covered 

 with a hyaline membrane, in which, however, a fibrous structure 

 may be made out (Koganeï). 



