366 



SPECIAL HISTOLOGY. 



pass directly into the vena vorticosae ; 2. internal, which pass 

 into a capillary plexus immediately beneath the pigment, in 

 the so-termed membrana choriocapillaris, or Ruyschiana; and 



Fig. 301. 



3. anterior, which are continued into the 

 ciliary body and iris. The above mentioned 

 capillary plexus of the innermost layer of the 

 choroid — which in animals having a tapetum 

 lies upon its internal aspect, and may easily 

 be demonstrated as a special membrane, as 

 may also occasionally be done in Man — is 

 one of the most elegant and closest that 

 exists, inasmuch as its meshes, formed by 

 vessels of 0004'", do not measure more than 

 0-002— 0-005'", the capillaries arising from 

 the larger vessels, as it were in a stelliform 

 manner. It extends, as has been already said, 

 only as far as the ora serrata, where it gives place 

 to somewhat coarser convolutions of vessels, 

 0*004"' in diameter, which, proceeding from 

 the anterior branches of the short posterior 

 ciliary arteries, constitute the ciliary processes, 

 and are so closely approximated that, besides 

 the vessels and a homogeneous sheath supporting the processes, 

 the latter seem to contain no other tissue. From these various 

 points and from the ciliary muscle, which likewise obtains some 

 twigs from the same arteries, the blood is returned principally 

 through the venae vorticosae, which, lying upon the arteries, 

 constitute elegant vascular stars or vortices, two above and 

 two below (or it may be five or six) ; and also at the back of 

 the eye- ball, through some minute vena ciliares posticce breves, 

 all of which veins penetrate the sclerotic in the same way as 

 the arteries. 



The iris receives its blood in the first place from the arteries 

 of the choroid, and secondly from the long posterior and 

 the anterior ciliary arteries. The former, with their anterior 



Fig. 301. Vessels of the choroid and iris of a Child, after Arnold; viewed from 

 within, x 10 diam.: a, capillary plexus of the posterior segment of the choroid, ter- 

 minating at the ora serrata, b ; c, arteries of the corona ciliaris, supplying the 

 ciliary processes, d, and in part passing upon the iris, e ; f, capillary plexus on the 

 inner surface of the pupillary margin of the iris. 



