14 A TYPICAL VERTEBRATE EYE: THE HUMAN 



and the ora terminalis, a fairly smooth posterior region in the ciliary 

 body, called the orbiculus ciliaris (Fig. 3 ; Fig. 5, oc; Figs. 6c, 7g, cor, orb) . 

 Inasmuch as it is from the blind epithelial part of the retina covering 

 the ciliary body that the aqueous humor is given off, the ciliary processes 

 and the less conspicuous secondary folds between them are best inter- 

 preted as a device for greatly increasing the secretory surface for the 



MiS 







spca 

 spcv 



Fig. 6 — Vascular structures of the human eye. 



a, vascular plan of the eye, showing veins in black, arteries clear. Modified from Adler, 

 after Leber. 



dcv- anterior ciliary vessels; cc- choriocapillaris; crv- central retinal vessels; c/- canal of 

 Schlemm; ey- episcleral vessels; Ipca- long posterior ciliary artery; mc- major circle of iris; 

 pcy- posterior conjunaival vessels; rca- recurrent chorioidal artery; rv- retinal vessels; spca- 

 short posterior ciliary artery; spcv- short posterior ciliary vein; yep- vessels of ciliary process; 

 y'l- vessels of iris; yns- vessels of optic nerve and sheath; yy, yy- vorticose veins. 



b, surface view of portion of choriocapillaris from fundus, x 65. Redrawn from Salzmann. 

 The black spots mark the junaions, with the capillary net, of small connecting arteries and veins. 



c, surface view, from inner side, of portion of ciliary body. After Franz. 



c- cornea; ch- ciliary body; cor- corona ciliaris; cp- ciliary processes; /, /- minor folds; ;'- iris; 

 orh- orbiculus ciliaris; r- retina; s- sclera. 



production of aqueous. This was probably not their primary function 

 when they were originally evolved, however, as will be seen later when 

 the method of accommodation in the reptiles is explained. Over the cili- 

 ary body, the blind pars ciliaris retinae consists of a double layer of tall 

 cells, the ciliary epithelium (Fig. 7g, ce, ce). The outermost of these 

 layers is pigmented and is a simple continuation of a similar pigmented 

 layer which, further posteriorly, lies between the chorioid and the sensory 



