CHAPTER XVIII. 







THE EYE. 



THE organ of sight is composed of the eyeball 

 and various accessory structures, such as the eyelids, 

 lachrymal gland, muscles, etc. The eyeball is com- 

 posed, in the first place, of a dense, firm, spheroidal 

 connective-tissue envelope, whose anterior transpar- 

 ent portion, the cornea, is more convex than the 

 posterior opaque segment, the sclerotic, and differs 

 somewhat from it in structure ; the sclerotic is 

 pierced posteriorly by the optic nerve. Within the 

 sclerotic lies a vascular tunic, the clioroid, formed of 

 several layers of tissue, and thrown anteriorly, just 

 behind the sclero-corneal junction, into numerous 

 longitudinal folds, called the ciliary processes. An 

 extension from the ciliary processes passes forward, 

 constituting the iris, which is a perforated vascular 

 connective-tissue and muscular curtain, suspended 

 behind the cornea, and connected peripherally, near 

 the sclero-corneal junction, with a connective-tissue 

 structure called the ligamentum pectinatum. 



Passing backward from the ligamentum pectina- 

 tum, between the ciliary processes and the sclera, 



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