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sclerotic. The ophthalmic artery breaks up in the choroid 

 gland. The other artery appears to pass forwards with 

 the optic nerve to the retina, but we are uncertain as to its 

 precise distribution. 



The sclerotic consists of two layers, an external layer 

 of tough fibrous tissue into which the eye muscles are 

 inserted, and an internal cartilaginous layer of some thick- 

 ness. The cartilaginous sclerotic is perforated for the 

 entrance of the optic nerve and the blood vessels, the 

 fibrous layer becoming continuous with the connective 

 tissue surrounding the latter structures. The cartilaginous 

 sclerotic ceases at some distance from the pupil, and the 

 fibrous layer with another layer which seems to be a con- 

 tinuation forwards of part of the choroid fuse with the 

 skin of the head to form the cornea. In suitably prepared 

 sections all these layers can be distinguished in the cornea, 

 and the structure of the skin in that region does not differ 

 materially from that in other parts of the head. 



The Argentea. — Internal to the sclerotic and in close 

 contact with its internal surface is the peculiar layer so 

 named. It covers the whole internal surface of the 

 sclerotic as far forwards as the iris. It has a white silvery 

 appearance by reflected light, but is opaque to trans- 

 mitted light. IS o structure beyond wavy bundles of very 

 fine fibres can be made out in it. The silvery appearance 

 is said to be due to minute crystals imbedded in a cellular 

 tissue. 



The Choroid. — This is the usual vascular and pig- 

 mented layer. It lies between the argentea and the 

 retina, is closely adherent to the latter, and comes away 

 with it when removed. Anteriorly it passes into the iris. 



The Choroid Gland. — This structure is situated in the 

 posterior wall of the bulb between the argentea and the 

 choroid. It lies to the nasal side of the entrance of the 



