54 3 



THE IRIS. 



[sect. 225. 



flattened, oblong corpuscles, o'0007"' in length at the most, which, 

 even within the cells, but more distinctly when they are free, 

 present in a well marked manner, the phenomenon of molecular 

 movement. — In the eyes of Albinos, and also, in a part at least, 

 of the eye of animals, in the region of the tapetum, the pigment 

 of the choroid is absent ; the cells, however, which usually contain 

 the pigment, are themselves present in both these cases, only they 

 are perfectly pale. 



The Iris differs from the choroid in containing a true connective 

 tissue, whose delicate loose bundles constitute the chief mass of 

 the stroma of the membrane ; their course is in part radiating, in 

 part circular, especially at the ciliary border, where they are 

 variously interwoven with each other. Towards the surface of the 

 iris, these loose bundles become converted into a more homo- 

 geneous layer ; and in this there occurs, 1, a great number of cells, 

 or plasmatic cells, frequently containing pigment, and mostly 

 fusiform and stellate, more rarely roundish in shape ; some of these 

 anastomose in a reticulate manner ; 2, a small number of pale, rigid 

 fibres like elastic fibres, which extend as processes of the ligamen- 

 tum iridis pectinatum, or of Denwurs' membrane, over a part of 

 the anterior surface as far as to the annulus minor ; 3, lastly, the 



smooth muscular fibres of the iris, 

 s which are exactly of the same nature 

 as those of the choroid. These last 

 form in man a very distinct sphincter 

 muscle {sphincter pupillce) , in the form 

 of a smooth ring, J'" broad, situated 

 exactly at the pupillary border, and 

 somewhat nearer the posterior surface ; 

 in a blue iris, this can readily be re- 

 cognised after the removal of the pos- 

 terior pigment, either before or after 

 the employment of acetic acid ; and it 

 can also be separated into its elements, 

 CV02'" to o , 03" / in length. Besides this 



Fig. 221. 



A part of the sphincter and dilator 

 pupillaa of the white rabbit, treated 

 with acetic acid ; magnified 350 times. 

 a. sphincter ; 6. fasciculi of the di- 

 lator; c. connective tissue with plas- 

 matic cells, which has become trans- 

 parent. 



larger muscular ring, I find in the 



region of the annulus iridis minor, 

 another very narrow muscular ring, 

 £§" in breadth, and nearer to the an- 

 terior surface of the iris. I have not 

 yet, like Brilcke, traced the dilator pupillce up to the lig amentum 

 pectinatum, and to the border of the vitreous lamella of the 



