THE EYE. 337 



nea over a circular space which would entirely cover these 

 probable channels of exit. 



Preparations of these parts can be made from eyes which 

 have been placed in Miiller's fluid while quite fresh and al- 

 lowed to remain in it three to four weeks, the fluid being re- 

 newed from time to time. Hsematoxylon is well adapted for 

 coloring them, and they may be preserved in glycerine. 



The solera. In the sclera we find the same minute struc- 

 tures as in the cornea, i.e., bundles of fibres, cementing sub- 

 stance, lymph-spaces, and fixed corpuscles. The fibres, how- 

 ever, are not laminated, as in the cornea, but run in various 

 directions, weaving a very dense tissue, so that the lymph- 

 canals have a correspondingly tortuous course. 



Chemically there is a difference between the two, as the 

 sclera is found to yield on boiling a true connective-tissue 

 gelatine ; the cornea, on the other hand, a substance resem- 

 bling chondrine. We find also in the sclera, near the foramen 

 for the optic nerve, a few pigment-cells. 



The sclera is covered by the conjunctiva from the corneal 

 border to the insertion of the recti muscles, and the fibres of 

 the subconjunctival tissue pass directly into it. From the en- 

 trance of the optic nerve to these muscular insertions, and even 

 passing up between them, the scleral portions of Tenon's cap- 

 sule form the covering, which consists of delicate filaments of 

 connective tissue passing directly into the sclera itself. On the 

 inner surface the sclera is covered with a large-celled endothe- 

 lium lining the perichoroidal space. At the round opening 

 for the entrance of the optic nerve, the outer fibres of the optic 

 nerve sheath pass directly into the outer scleral layers ; the 

 inner portions of the sheath partly mingle with the inner 

 layers of the sclera, and partly, after the addition of some true 

 scleral fibres, form the lamina cribrosa, a fine, sieve-like net- 

 work of fibrous tissue, which stretches across the opening in 

 the sclera on a level with its inner surface. This lamina can 

 be easily shown in specimens where the delicate nerve-fibres 

 .which pass through its openings have been macerated out. 



The sclera is perforated in the equatorial region by the 

 trunks of the vena vorticosce ; they are accompanied by the 

 lymph-vessels which form the connection between the pericho- 

 roidal and Tenon's lymph-spaces. The direction of the canal 

 through which they pass is so oblique that it is supposed to be 



