570 THE EYE 



The lamina fusca near the posterior pole is firmly adherent to the 

 scleral substance. 



At the posterior pole of the eye the sclera is pierced by the 

 optic nerve, whose numerous bundles penetrate the coats of the 

 eyeball and give to this portion of the sclera a cribrous appearance. 

 This area of the sclerotic coat is known as the lamina cribrosa scle- 

 rce. It is a circular zone whose border is outlined by the entrance 

 of the posterior ciliary arteries and the ciliary nerves. This is the 

 thickest portion of the sclera, the coat becoming progressively thin- 

 ner toward the equator of the eye ; near its anterior margin it is 

 again thickened by the tendinous insertions of the extrinsic muscles. 



The sclera is chiefly supplied by branches from the posterior 

 ciliary arteries, which form a wide-meshed plexus in its substance, 

 its vessels anastomosing freely with those of the choroid coat. 



The sclero-corneal junction (Fig. 422) is a narrow circular zone 

 at the margin of the cornea, where it is inserted into the sclera. 

 Across this narrow zone the fibrous bundles of the opaque sclera 

 are continued directly into the similar, though perfectly trans- 

 parent, bundles of the corneal substance. 



The anterior or outer surface of this zone is covered by the 

 ocular portion of the conjunctiva. Its epithelium is of the strati- 

 fied, squamous variety and is continuous with the anterior epi- 

 thelium of the cornea. 



From the inner surface of this junctional zone the anterior 

 extremities of the muscle fibres composing the ciliary muscle take 

 their origin. The fibres of this muscle intermingle with the mar- 

 ginal fibres of the posterior homogeneous layer of the cornea to 

 form the ligamentum pectinatum, which connects the sclero-corneal 

 junction with the base of the iris. 



Toward the inner side of the scleral margin and near the border 

 of the cornea is the canal of Schlemm. The nature and function 

 of this canal are somewhat uncertain. It frequently contains blood 

 cells, but also appears to be in direct communication with the nu- 

 merous lymphatic spaces of Fontana, which lie in the lateral wall of 

 the anterior chamber and between the fibre bundles of the ligamen- 

 tum pectinatum. The spaces of Fontana are true lymphatic spaces 

 and are in communication with the anterior chamber of the eye. 



Blood Supply. The sclero-corneal junction is abundantly sup- 

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

 posterior conjunctival vessels, form loops at the margin of the cor- 

 nea and anastamose freely with the vessels of the ciliary body. 



