TIIEEYE. 77 



tiou, corresponding to the sclerotic, and which is called the 

 choroid ; an anterior portion opposite the cornea, called 

 the iris ; and an intermediate ring on a level with the union 

 of the sclerotic and cornea, consisting of the ciliary muscle 

 and processes. 



To show the choroid, the sclerotic is to be cut through just behind 

 the cornea, and from this circular incision three or four slits are to be 

 made with the scissors toward the optic nerve; the resulting flaps 

 are then to be carefully reflected. In another eye the cornea should 

 be removed and the iris gently torn away with the forceps ; this will 

 expose the ciliary processes. 



The CHOROID is a thin pigmentary membrane, extending 

 from the optic nerve, which perforates it, to the anterior 

 part of the eyeball, as far forward as a white ring at the 

 line of union between the sclerotic and cornea, which is the 

 ciliary muscle ; at this point the choroid bends inward 

 behind the iris to end in a series of plaited folds, called 

 the cilia ry processes^ arranged around the lens in the form 

 of a circle. The pigment of the choroid is principally con- 

 tained in an internal epithelial layer, and is easily detached 

 and washed away. In many animals, at the bottom of the 

 eye, there is a brilliant arrangement of fibres on the internal 

 surface of the choroid, which shines with a metallic lustre, 

 and is called the tapetum oculi. 



The CILIARY LIGAMENT, or, as it is now more properly 

 termed, the CILIARY MUSCLE, will be seen as a white ring 

 sometimes called the armulus albidus, situated outside that 

 part of the choroid which turns inward to form the ciliary 

 processes, and opposite the junction of the cornea and scle- 

 rotic coats. The ciliary muscle constitutes the most anterior 

 part of the choroid; its muscular character is not capable 

 of demonstration in an ordinary dissection, but it fulfils 

 an important office in connection with the sense of vision. 

 Between the ciliary muscle and the sclerotic is a minute 

 vascular canal called the canal of Schlemm, sometimes also 

 of Font ana. 



The IRIS is a vascular and muscular structure, sufficiently 

 displayed in the dissections already made; it is circular in 

 form, and is suspended vertically in front of the crystalline 

 lens ; its anterior surface is free in the aqueous humor, and 

 marked by lines converging toward the pupil; its posterior 

 surface is covered by a thick la}^er of pigment, to which 

 the name uvea has been applied, and is in contact with 

 the lens ; its circumference corresponds to the point at 



7* 



