338 



NORMAL HISTOLOGY. 

 THE FIBROUS TUNIC. 



The Sclera. The sclera, or sclerotic coat, is a firm, dense fibrous 

 tunic which forms the posterior five-sixths of the outer coat of the eye, being 

 closely connected with the sheaths of the optic nerve posteriorly, and joining 

 in front with the cornea. In the neighborhood of the optic nerve it measures 

 i mm. in thickness, gradually becoming thinner towards the equator, until, 

 just posterior to the attachment of the tendons of the ocular muscles, it 

 measures only .4 mm. After receiving the expansions of these tendons it 

 increases and reaches a thickness of .6 mm. The optic nerve passes through 

 this tunic at a position i mm. below and from 2.5-3 mm - to tne inner side o* 



Fibre layer 

 Ganglion-cells 

 Bipolar cells 

 Visual cells 



Pigment layer 



Strom a 

 Large vein 



Lamina fusca 



Fibrous tissue 

 of sclera 



Episcleral 

 endoihelium 

 Space of Tenon 

 between sclera 

 and capsule 

 of Tenon 



FIG. 384. Section through posterior wall of eyeball, showing relative thickness of the fibrous, vasculat 



and nervous coats. X 40. 



the posterior pole of the eye; the canal is partially bridged over by inter- 

 lacing fibrous bundles, the lamina cribrosa, which are intimately associated 

 with the supporting tissue of the nerve. 



The sclera is composed of interlacing bundles of white fibrous tissue, 

 which in the outer and inner layers have chiefly a meridional direction, while 

 the central bundles are alternately circular and meridional. With the fibrous 

 bundles is associated a rich network of fine elastic fibres. The clefts between 

 the lamellae contain irregularly stellate connective tissue cells, the scleral cor- 

 puscles. On the inner surface of the sclera many of these cells are pig- 

 mented and give it a brownish color. This layer, the lamina fusca, with the 

 underlying choroid encloses a narrow cleft, the suprachoroidal lymph-space, 

 both walls of which, together with the fine connective tissue trabeculae which 

 cross it, are lined with endothelial cells. The outer surface of the sclera, 

 from the optic nerve entrance to the attachment of the ocular muscles, is 



