THE EYE. 



823 



covered by a very thick layer of pigment named the uvea: portions of 

 which, supported by a small pedicle, frequently pass through the 

 pupillary aperture and appear in the anterior chamber of the eye, where 



Fig. 386. 



Fig. 387. 



THE EYE (HUMAN) WITH THE SCLEROTIC COAT REMOVED. 



1 4 Sclerotic coat ; 2, Veins of the choroid ; 3, Ciliary nerves ; 4, Veins of the 



choroid ; 5, Ciliary ligament ; 6, Iris. 



they are known as "soot-balls" or corpora nigra. (There are frequently 

 several of these black spongy masses, which are generally attached to the 

 upper border of the pupil ; on the lower margin, when present, they are 

 much smaller. Their colour is a brownish-black. They are sometimes so 

 large as to give rise to apprehensions of injury to the vision.) 



The larger circumference of the 

 iris is attached to the ciliary liga- 

 ment, which unites it to the 

 choroid; it is also related to the 

 margin of the cornea, as well as to 

 that of the sclerotic opening. 



The lesser, or internal circum- 

 ference, is elliptical, and circum- 

 scribes the pupillary aperture. 



STRUCTURE. The organisation 

 of the iris has been much dis- 

 cussed ; but at present it is ad- 

 mitted that its principal element 

 is unstriped muscular fibre. A 

 proper membrane and two epi- 

 thelial layers enter into its form- 

 ation. The proper membrane has, 

 for its framework, circular or radia- 

 ting fasciculi of wavy connective 

 tissue, with pigment cells. Be- 

 tween the fasciculi are placed the a > Sphincter of the pupil ; 6, 6, Radiating fasciculi 

 unstriped fibres ; these are disposed of dilat01 ; muscle ; c, c, Connective tissue with 

 in a circular manner around the corpuscles. 



pupil to constitute the pupillary sphincter, and others radiate from the lesser 



MUSCULAR STRUCTURE OP THE IRIS OF A 

 WHITE RABBIT. 



