PRACTICAL CONSIDERATIONS : THE VASCULAR TUNIC. 1459 



pigmented cells, but in the white races is free from pigment. In hyperopic eyes the 

 circular bundles are usually better developed than in myopic ones. 



The blood-vessels of the ciliary body arise from the anterior and the long ciliary 

 arteries. They form a ring around the root of the iris, the drculus arteriosus iridis 

 major, from which vessels are sent inward to supply the iris, ciliary muscle and 

 ciliary processes. The veins from the ciliary muscle empty chiefly into the anterior 

 ciliary veins; those from the ciliary processes, and a few from the ciliary muscle pass 

 backward and become tributary to the vents vorticosce. 



The nerves of the ciliary body are derived from the anterior branches of the long 

 and short ciliary nerves, which form an annular plexus within the ciliary muscle. 

 Four sets of fibres probably exist : ( i ) sensory fibres, largely subscleral in distribu- 

 tion ; (2) vasomotor fibres running to the blood-vessel walls ; (3) motor fibres sup- 

 plying the muscle bundles ; (4) fibres terminating within the interfascicular tissue of 

 the ciliary muscle. 



Practical Considerations. Congenital coloboma of the choroid, as of the 

 iris, usually occurs in the lower part, along the line of the foetal ocular cleft. In the 

 defect the sclera shows pearly white through the ophthalmoscope, with here and 

 there a little pigment and a few ciliary vessels. The retina is frequently absent, but 

 its occasional presence explains why this area is not always blind. 



In acute exudative inflammation of the choroid, foci of inflammation are seen 

 scattered over the fundus, and are characteristic. They form yellowish spots between 

 the choroid and retina, and are later converted into connective tissue, binding the 

 choroid and retina together. The two layers become atrophic finally, the layers of 

 rods and cones disappearing. The exudate may extend into the retina and even into 

 the vitreous, producing opacities. 



Sarcoma is the common tumor of the choroid and is usually pigmented. 



Carcinoma of the choroid is always a metastatic growth, usually a metastasis from 

 a carcinoma of the breast. Adenoma, angioma, and enchondroma of the choroid 

 have been described. 



The Iris. The iris forms the anterior segment of the vascular tunic and is 

 visible through the cornea. Slightly to the inner side of its centre is placed an 

 approximately circular 



opening, the pupil. The FIG. 1216. 



periphery of the iris, or 

 ciliary border, is attached 

 to the ciliary body behind 

 and receives fibres from 

 the pectinate ligament an- 

 teriorly. The free border, 

 which forms the margin 

 of the pupil, rests upon 

 the anterior surface of the 

 lens. The iris measures 

 1 1 mm. in diameter and 

 about .4 mm. in thick- 

 ness. The pupil varies from i-S mm. in diameter. The color of the iris, viewed 

 from in front, varies in different individuals and gives the color to the eyeball. It is 

 dependent partly upon the amount of pigment within the iris stroma, and partly 

 upon the density of the pigmentation of the cells on its posterior surface. In light 

 blue eyes, the stroma contains very little pigment and the posterior pigment layer, 

 seen through it, gives it a bluish tint ; whereas in brown eyes the stroma contains so 

 much pigment that the posterior pigment layer is totally obscured and the iris appears 

 brown. The anterior surface is marked by a number of fine, radiating lines, or ridges, 

 which indicate the position of the blood-vessels. Concentric to the pupillary margin, 

 at a distance of from i-2 mm., is an irregular ridge, the drculus arteriosus iridis 

 minor, which divides the iris into a pupillary and a ciliary zone which are often differ- 

 ently colored. The pupil is surrounded by a narrow black border. The posterior 



Pupillary margin Anterior endotheliu 



Sphincter muscle Pigmented pars iridica retinae 



Section of pupillary end of iris. X 210. 



