I5i6 A MANUAL OF ANATOMY 



In other eyes pigment is contained in the cells of the two 

 layers of columnar epithelium which line the posterior surface of 

 the iris, and form the pars iridica retinae (uvea). In blue eyes the 

 pigment is confined to this region, but in dark coloured eyes (black, 

 grey, or brown), it is also present in the brajiched cells of the con- 

 nective-tissue stroma. 



Blood-supply — Arteries. — ^The arteries of the iris are derived 

 from (i) the long ciliary, and (2) the anterior ciliary, vessels. 



The long ciliary arteries are two in number, and belong to the 

 posterior ciliary group of branches from the ophthalmic artery. 

 They pierce the back part of the sclerotic, one on each side of the 

 optic nerve, and pass forwards between the sclerotic and the choroid 

 towards the ciliary margin of the iris. Here each vessel divides 

 into two branches, upper and lower, which anastomose with those 

 of the opposite side to form an arterial ring round the ciliary margin 

 of the iris, called the circulus major. This ring is joined by some 



Long Ciliary Artery 

 Anterior Ciliary Artery ,^-->==:::-^^ Short Ciliary Artery 



Arteries of Iris ,, ^j. r-^^u ^r-^^=»^ -•^tuins^.x « . , « , 



Portion of Sclerotic 



Optic Nerve 



__^ _ Short Ciliary Arteries 



Pupil "'" 



Ciiculus Major 



Fig. 630. — The Arteries of the Choroid and Iris (Lateral View). 



of the anterior ciliary arteries, and it gives offsets to the ciliary 

 muscle and iris. The branches which enter the iris are supported 

 by the connective-tissue stroma, and converge towards the pupillary 

 margin, near which they form by their anastomoses another arterial 

 ring, called the circulus minor. 



The anterior ciliary arteries are about six in number, and are 

 derived from the muscular and lachrymal branches of the oph- 

 thalmic artery. They are of small size and pierce the anterior 

 part of the sclerotic, close to the corneo-scleral junction. Some 

 of them supply the ciliary processes, and others join the circulus 

 major. 



The veins of the iris accompany the arteries, and are in com- 

 munication with the canal of Schlemm. 



Nerves of the Choroid Coat and Iris. — These are derived from 

 the ciliary nerves, short and long, the former coming from the 

 ciliary ganglion, and the latter from the nasal branch of the 



