1460 



HUMAN ANATOMY. 



FIG. 1217. 



Pupillary border of iris- 



Lesser arterial circle 



Ciliary artery 



Vascular plexus in 

 ciliary processes " 



Veins draining 

 ciliary processes 



surface of the iris presents a series of delicate converging folds, which are intersected 

 by concentric lines. 



Structure of the Iris. Radial sections of the iris show the stroma to be com- 

 posed of numerous thick-walled blood-vessels, running in a radiating manner from the 

 ciliary border toward the pupil. They are supported by a delicate connective tissue 

 framework, which contains irregularly shaped, branching pigmented cells, many 

 nerves and lymph-spaces. The anterior surface is covered with a single layer of polyg- 

 onal cndothelial cells, continuous with those lining Descemet's membrane. Beneath 

 these cells is a condensation of the connective tissue stroma the anterior boundary 

 layer, in which the cells are closely placed. Minute clefts in the tissue form a direct 

 communication between the anterior chamber and the interfascicular lymph-clefts. 

 In very dark irides pigment is found not only within the branched cells, but heaped 

 in irregular masses within the stroma. The muscular tissue of the iris consists 



of two distinct masses, the 

 sphincter pupilla and the dila- 

 tator pupillce. 



The sphincter muscle, is 

 a band of involuntary muscle 

 measuring about .7 mm. in 

 width, which surrounds the 

 pupil and is situated in the 

 vascular stroma, back of the 

 blood-vessels, and separated 

 from the pupil edge by the 

 narrow border constituted by 

 the posteriorpigmented layer. 

 The dilatator muscle is 

 formed by a sheet of smooth 

 muscle-fibres in the position 

 formerly described as the 

 posterior limiting lamella, or 

 membrane of Bruch. The 

 investigations of Grynfeltt 

 and Heerfordt have settled 

 definitely the question of its 

 existence, and shown that its 

 fibres arise from the outer cells 

 of the retinal pigment layer, 

 on the posterior surface of the 

 iris. They do not reach quite 

 to the pupillary border. 



The posterior surface of 

 the iris is covered by the pig- 

 mented layer, which morphologically represents the anterior segment of the atrophic 

 nervous tunic, or pars iridica retina;. This is continuous with the pigmentary layer 

 covering the ciliary processes, but the cells, disposed as a double layer, are so deeply 

 pigmented as to be indistinguishable without bleaching the tissue. The dilatator 

 muscle is developed from the outer layer of fusiform cells, so that it represents an 

 epithelial (ectoblastic) muscle. The inner cells are larger polygonal elements, which 

 gradually lose their pigment as they approach the ciliary processes. Over the latter 

 they contain no pigment, whereas the outer cells remain pigmented. 



The blood-vessels of the iris pass radially inward from the circuhis arteriosus iridis 

 major at the periphery. Near the pupillary border, they form a second ring, the cir- 

 cnlus arteriosus iridis minor, branches from which supply the sphincter muscle and the 

 pupillary /one. The venous radicles unite to form trunks which accompany those 

 from the ciliary processes to empty into the vena; vorticosa;. 



The /vinp/iafics are represented by the interfascicular clefts which communicate 

 with the anterior chamber, with the spaces within the ciliary body, and with the 

 spaces of Fontana. 



Choroidal veins 



Injected ciliary processes and iris ; vessels are seen from the 

 posterior surface. X 30. 



