CHAP, vi DIOPTKIC MECHANISM OF THE EYE 



267 



The outer or fibrous coat (known to the ancients indifferently 

 as sclera, cornea, or dura) consists of two distinct parts : an 

 anterior, transparent portion, the cornea, and a posterior, opaque 

 part, the sclerotic. The middle coat, or uvea (from its likeness 



Epithelium 



Canalis 



Pars ciliaris '-/X^V^S^-^" ^^^///l#r Liqarnentum ^^^.f Arteria ciliaris anf. 

 retinae \ ^^ 3%^ SU spensorium WV 



Vena vorticosa 



Arteria centralis 

 retinae "* V| " 



"Qural sheath 



FIG. 106. Diagram of the adult right human eye, horizontal section. Magnified 5 times. (Luciani 

 from A. E. Scha'fer.) The line a 6 passes through the equator, x y through the optic axis of 

 the eye ; A.c.p., posterior ciliary artery ; A.c.a., anterior ciliary artery ; N.c., one of the ciliary^ 

 nerves; V.v., vena vorticosa; e.r.m., external rectus muscle; o.c., anterior, p.c., posterior 

 chamber of the eye ; P.c., Petit's canal. 



to a black grape from which the stalk has been torn away), is 

 now subdivided into three portions a posterior, pigmented part, 

 the choroid; a middle region which is muscular and bears 

 papillae, the zona ciliaris ; and an anterior diaphragm formed by 

 the iris, the aperture in its centre being the pupil. The inner 

 coat, known as the retina, arachnea, or arachnoid, because it 



