310 TUNICA VASCULOSA, BY PROF. A. IWANOFF. 



number varies to a considerable extent. They are abundant 

 in certain intraocular pathological conditions. 



The external surface of the suprachoroid coat, according to 

 the recent researches of Schwalbe, is covered with an endo- 

 thelium. 



The question of the nature and kind of tissue of which the 

 choroid is composed cannot be determined exclusively on his- 

 tological grounds, but requires also an histogenetic investiga- 

 tion. The defective character of the latter has led some to 

 classify the strorna of the choroid with connective tissue, and 

 others with elastic tissue. 



II. THE IRIS. In the iris we distinguish the pupillary border, 

 margo pupillaris, bounding the central opening or pupil; and 

 the ciliary border, margo ciliaris, by which it is attached to 

 the ciliary body and the cornea. It has also an anterior and 

 a posterior surface. 



On the anterior surface of the iris is a dentated ridge which 

 divides it into two zones : the internal or pupillary zone, 

 about one millimeter broad, is beset with radiating folds in 

 close apposition to each other ; the external or ciliary zone has 

 a breadth of about three millimeters (with an average diameter 

 of the pupil of four millimeters in the dead body), and presents 

 in its peripheric half from five to seven concentrically arranged 

 folds, which always but especially when the pupil is dilated 

 project sharply denned. 



The anterior surface of the iris is covered by an epithelium, 

 which is really the continuation of the epithelium of the mem- 

 brane of Descemet, but differs somewhat from this in being 

 composed of smaller cells which are granular, not quite so dis- 

 tinctly hexagonal, and not so sharply differentiated from one 

 another. 



The posterior surface of the iris is black, consequent on the 

 presence of a thick layer of pigment. This is the uvea of 

 authors. The uvea begins at the margin of the pupil, which 

 when contracted is distinctly bordered by it (whilst when 

 dilated it vanishes entirely), and terminates at the ciliary border, 

 where it becomes continuous with the pigmentary layer of the 

 ciliary processes. The contour line between these two pig- 



