THE UVEAL TRACT 



a V abl pbl 



Fig. 7 — The iris. 



a, radial section of human iris, x 24. a- artery; at/- anterior border layer; c- crypt; «e- iris 

 epithelium (= pigmented posterior layer of iridic retina); ma- major circle (circular artery in 

 ciliary body); wj- minor circle (anastamosis of radial vessels); phi- posterior border layer 

 (= dilatator pupillee, = myoid lamina of anterior epithelial layer of iridic retina); pz.- pupil- 

 lary zone (remainder of iris constitutes ciliary zone); s- connective-tissue stroma; sm- 

 sphincter muscle; v- vein. 



b, =the small rectangle in a, enlarged to show the heavily pigmented posterior epithelium 

 and the lightly pigmented 'spindle cells' of the anterior epithelial layer, whose muscular 

 portions merge into a sheet to form the dilatator. Partly after Salzmann. 



c, a spindle cell from the anterior retinal layer of the iris of a rhesus monkey, showing the 

 epithelioid cell-body and the partial differentiation of the base of the cell into a muscle 

 fiber, which is shown in its contracted condition. Redrawn, modified, after Hotta. d, same 

 as c, relaxed, e, same as c, but stretched (as when sphincter contracts). 



f, diagram of vascular plan of mammalian iris, showing veins in black, arteries clear. 

 cp- capillary plexus of pupillary zone (devoted particularly to the sphinaer muscle); Ipca, 

 Ipcd- long posterior ciliary arteries; ma- major circle; wi- minor circle. 



g, diagram showing distribution of pigment (stippling) in the retinal portion of the iris, as 

 compared with that in the ciliary epithelium and in the region of the sensory retina. 

 ce, ce- ciliary epithelium; cor- corona ciliaris; cp- ciliary process; ie- iris epithelium; o- era 

 termmalis of sensory retma; orb- orbiculus ciliaris; pbl,sc- piosterior border layer ( = dila- 

 tator) and spindle cells; pe- pigment epithelium of sensory retina; s- sclera; sm- sphincter 

 muscle; sr- sensory retina; u, u- uvea. 



