HEAD. 8T 



covered by the muscles and adipose tissue, the internal 

 lined by the clioroid. The anterior 0})ening is contin- 

 uous with the cornea, the posterior is run through by 

 the optic nerve. Structure : connective tissue mixed 

 with elastic fibres and pigment. 



2. Cornea. — Two surfaces and a circumference. 

 Structure: three layers ; an external, the conjunctival 

 epithelium ; a middle, composed of fasciculi of con- 

 junctival fibrilla, between which is a liquid amorphous 

 substance ; and an internal, portion of the membrane 

 of the aquous humour. 



3. Choroid. — Divided by the ora serrata into two 

 zones, one posterior or choroid, internally in contact 

 with the retina and externally with the sclerotic ; one 

 anterior or ciliary, formed by ciliary circle, and a ciliary 

 body, from which hangs the ciliary processes. Structure : 

 four layers ; an external, composed of connective and 

 elastic fibres with pigmentary cells; a second layer, 

 vascular and nervous, with pigmentary cells ; a third 

 layer, or of Ruysch, formed of amorphous substance ; 

 and an internal layer, composed of hexagonal cells 

 containing pigment. 



4. Iris. — A septum in front of the crystalline lens, 

 with the pupil in its centre, through which appears 

 the " soot-balls " or corpora nigra, portions of the 

 uvea which covers the posterior face of the iris. 



