THE EYE AND ITS APPENDAGES 239 



THE BYE. 



The eye-ball is contained within the orbit; its shape is 

 spherical, with the segment of a smaller sphere, corresponding 

 to the cornea, superimposed anteriorly. 



The eye-ball consists of three coats enclosing three re- 

 fractive media : 



IChoroid. 

 Ciliary body. 

 Iris. 

 yd coat ... ... ... Retina. 



The refractive media are : 



1. Aqueous humour. 



2. Vitreous body. 



3. The lens. 



Covering the posterior of the eye-ball is a layer of fascia, 

 the capsule of Tenon, continuous posteriorly with the sclerotic 

 at the entrance of the optic nerve, whilst anteriorly at the 

 corneo-sclerotic junction it is connected with it by loose tissue 

 only, and is pierced by the tendons of the muscles of the eye- 

 ball. It is connected with the eye-ball only by delicate con- 

 nective-tissue, the interval constituting an extensive lymph- 

 spa^e and forming a free socket in which the eye-ball glides. 



The sclerotic coat is opaque and fibrous, and occupies the 

 posterior of the eye-ball, being continuous in front with the 

 cornea, at the corneo-sclerotic junction. 



The outer surface is white and smooth, receiving the inser- 

 tions of the recti and obliqui muscles. 



The inner surface is of a light-brown colour, due to a lining 

 of pigmented connective-tissue, the membrana fusca, which is 

 connected by fine filaments to the choroid coat. Between 

 the sclerotic and choroid coats is a lymph-space transmitting 

 branches of the ciliary vessels and nerves. 



The optic nerve passes through the posterior part of the 

 sclerotic, about $ inch internal to the axis of the eye-ball, the 

 point of perforation being called the lamina cribrosa. At its 

 entrance, the outer sheath of the nerve blends with the 

 sclerotic coat. 



The sclerotic is thickest at its posterior part, gradually 

 thinning until about inch from the cornea, where it thickens 

 hgain. 



