THE VASCULAR TUNIC 867 



pupillaris) surrounds the pupil. Its upper part bears in its middle several black 

 masses of variable size, termed the granula iridisi; similar, but much smaller, 

 projections may be seen on the lower margin of the pupil. The anterior surface 

 (Facies anterior) is usually dark brown in color; it presents fine folds (Pliea; iridis), 

 some of which are concentric with the pupil, others radial; they fade out near the 

 pupil. 2 The smooth, narrow, central part is termed the annulus iridis minor, while 

 the much broader plicated part is the annulus iridis major. The posterior surface 

 (Facies posterior) is usually black; the color is caused by a layer of pigmented 

 cells which is regarded as part of the retina. It presents numerous fine radial lines 

 except at the pupillary margin. Its central part is in contact with the anterior 

 surface of the lens, but peripherally the two are separated by a narrow space 

 termed the posterior chamber. The iris consists chiefly of the stroma iridis, a 

 delicate framework of connective tissue which supports numerous blood-vessels, 

 and contains branched pigmented cells. The muscular tissue is unstriped and 

 consists of a sphincter and a dilator of the pupil. The sphincter pupillse lies in 

 the posterior part around the pupil, with which the fibers are largely concentric. 

 The dilatator pupillae consists of fibers which radiate from the sphincter to the 

 ciliary border. The anterior surface of the iris is covered by a continuation of the 

 endothelium of the cornea. Beneath this is a condensation of the stroma, in which 

 the cells are close together and are full of pigmented granules.^ There appear to 

 be minute clefts here by which the lymph-spaces of the stroma communicate with 

 the anterior chamber. 



The arteries of the vascular tunic come from the ciliary branches of the oph- 

 thalmic artery. The arteries of the chorioidea are derived chiefly from the short 

 posterior ciliary arteries. These (four to six in ntunber) perforate the sclera around 

 the posterior pole, run forward in the lamina vasculosa, and form the rich capillary 

 network of the choriocapillaris. The two long ciliary arteries perforate the sclera 

 obliquely near the optic nerve; they run forward in the lamina suprachorioidea in 

 the horizontal meridian, one on the medial, the other on the lateral side of the 

 eyeball. On reaching the ciliary body each divides into two diverging branches; 

 the subdivisions of these unite with each other and with twigs of the anterior ciliary 

 arteries, thus forming near the periphery of the iris the cir cuius arteriosus major. 

 From this branches go to the ciliary muscle and processes and to the iris. The 

 branches in the iris run toward the pupillary margin, and by anastomotic branches 

 form an incomplete circulus arteriosus minor. The two anterior ciliary arteries, 

 dorsal and ventral, form an episcleral plexus around the corneo-scleral junction, 

 and give off branches which perforate the sclera. These supply twigs to the ciliary 

 muscle and recurrent branches to the chorioid, and assist in forming the circulus 

 arteriosus major. The blood is carried away from the vascular tunic chiefly by four 

 or five venous trunks, the venae vorticosae, which are formed by the convergence in 

 whorls of numerous veins from the chorioid, the ciliary body, and the iris. The 

 vena vorticosae perforate the sclera about at the equator and join the veins of the 

 ocular muscles. 



The nerves come from the long and short ciliary nerves. They form a plexus 

 in the lamina suprachorioidea, which contains ganglion cells, and sends numerous 

 non-medullated fibers chiefly to the blood-vessels of the chorioid. At the ciliary 

 muscle a second plexus (P. gangliosus ciliaris) is formed, which supplies the muscle 

 and sends fibers to the iris. The sphincter pupillee is supplied by fibers derived 

 from the oculomotor nerve, while the dilatator pupillaj is innervated by the sym- 

 pathetic. 



1 Also known as corpora nigra. 



2 Some of these folds are permanent, while others are temporary, i. e., produced by contrac- 

 tion of the iris. 



3 In albinos the pigment is absent here, as elsewhere, and the iris is pink in color. 



