636 THE EYE 



sive increase of infra-ocular tension which causes atrophy of the optic 

 nerve and the retina. 



Blood Supply. --The sclerocorneal junction is abundantly supplied 

 with blood from the anterior ciliary vessels, which, with the posterior 

 conjunctival vessels, form loops at the margin of the cornea and anasto- 

 mose freely with the vessels of the ciliary body. The sclera contains no 

 true lymphatic vessels. 



THE MIDDLE COAT THE VASCULAR TUNIC 



The middle tunic (uvea, uveal tract) includes the choroid coat, 

 ciliary body, and iris. The latter is perforated centrally by an approxi- 

 mately circular aperture, the pupil. 



The iris divides the cavity of the anterior segment of the eye into an 

 anterior chamber, included between it and the posterior or inner surface 

 of the cornea, and a posterior chamber, which is bounded by the iris in 

 front and the crystalline lens and its suspensory ligament behind. 

 The free or pupillary margin of the iris is in light contact with the 

 anterior surface of the lens. The posterior chamber is therefore an an- 

 nular compartment. 



THE CHOROID COAT 



The choroid coat (tunica choroidea) consists of three layers: 1, the 

 lamina suprachoroidea ; 2, the lamina vascularis ; 3, the lamina capillaris. 

 The function of the very vascular choroid is to supply nutrition to the 

 outer portions of the retina. 



The lamina suprachoroidea (suprachoroid layer) is a very delicate 

 membrane which contains many pigmented cells and is similar in struc- 

 ture to the lamina fusca of the sclera. 



The flattened pigmented cells are brownish-black in color from the 

 many coarse granules which they contain, and are irregularly disposed, 

 either separately or in groups. Lymphatic spaces occur between this 

 layer and the sclera and communicate through the interfascicular lym- 

 phatic clefts of the sclera with the capsule of Tenon. 



The fibers of this layer are not only distributed in its own plane but 

 pass obliquely to the lamina fusca, thus loosely attaching the supracho- 

 roid layer to the sclera. Similar, obliquely disposed fibers pass to the 

 deeper portions of the choroid, with the fibers of which they blend. 



The lamina vasculosa (vascular layer, choroid proper), so called 



