THE TUNICS OF THE EYE 



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the sulcus circularis cornese; it is bounded externally by the trabecular tissue 

 already described as forming the inner wall of the sinus venosus sclerse. Between 

 this tissue and the anterior surface of the attached margin of the iris is an angular 

 recess, named the iridial angle or filtration angle of the eye (Fig. 870) . Immediately 

 outside the filtration angle is a projecting rim of scleral tissue which appears in a 

 meridional section as a small triangular area, termed the scleral spur. Its base 

 is continuous with the inner surface of the sclera immediately to the outer side of the 

 filtration angle and its apex is directed forward and inward. To the anterior sloping 

 margin of this spur are attached the bundles of trabecular tissue just referred to; 

 from its posterior margin the meridional fibers of the Ciliaris muscle arise. 



Iris 



Sinus venous solera: 

 Trabecular tissue 



Cornea 



Scleral vein 



Radial muscular fibers 



of iris 

 Circular fibers of Ciliaris 



Meridional fibers of Ciliaris 

 cleral spur 



Iridial angle 



FIG. 870. Enlarged general view of the iridial angle. (Arthur Thomson.) 



Structure (Fig. 871). The cornea consists from before backward of four layers, viz.: (l\ 

 the corneal epithelium, continuous with that of the conjunctiva; (2) the substantia propria 

 (3) the posterior elastic lamina; and (4) the endothelium of the anterior chamber. 



The corneal epithelium (epithelium corneas; anterior layer) covers the front of the cornea and 

 consists of several layers of cells. The cells of the deepest layer are columnar; then follow two or 

 three layers of polyhedral cells, the majority of which are prickle cells similar to those found in 

 the stratum mucosum of the cuticle. Lastly, there are three or four layers of squamous cells, 

 with flattened nuclei. 



The substantia propria is fibrous, tough, unyielding, and perfectly transparent. It is com- 

 posed of about sixty flattened lamellae, superimposed one on another. These lamellae are made 

 up of bundles of modified connective tissue, the fibers of which are directly continuous with those 

 of the sclera. The fibers of each lamella are for the most part parallel with one another, but at 

 right angles to those of adjacent lamellae. Fibers', however, frequently pass from one lamella 

 to the next. 



