l6 s. IlOL'Iil AND O. liEKNER. M "N Kl. 



cubical or low cylindrical cells. In front of this then: i^ a layer of very 

 flat, long cell.s. The boundary between these two layers is very clear and 

 distinct, and that between the separate cells in the front layer — which 

 I will call the "muscle-epithelium layer" — appears also as a rule, but 

 not always, clear and distinct, although the greater part of it has not deve- 

 loped into contractile elements. This is perhaps due to the fact that the 

 cells appear to be fusiform (see fig. 8) or in any case somewhat pointed 

 at the ends (see fig. 7), for the majority of these cells are certainly long 

 enough to cover 4 or 5 of the cells in the hinder layer (see fig. 8). The 

 cells in this layer are cubical, while those in the front layer — the muscle- 

 epithelium layer — are long or at any rate oval. These long, flat cells 

 not infrequently contain 2, and sometimes 3, nuclei, which are occasionally 

 rounded, but generally elongated (see fig. 9, where one of the cells has 2 

 long nuclei). 



The characteristic feature of all these depigmented sections is the almost 

 entire absence of the Bruch's membrane. In depigmented sections of nor- 

 mal irises this membrane is always clear and distinct, even when the iris 

 has been kept stretched, for instance by the action ofeserine; butin these 

 sections it is absent almost always and almost entirely between the ciliary 

 body and the periphery of the sphincter. Behind this muscle, on the con- 

 trar}^ the membrane of Bruch is constant and continuous. 



When patches of developed dilatator are found between the ciliary 

 body and the periphery of the sphincter, they generally lie nearest to the 

 ciliary body. In fig. 6 I have marked with a cross ( + ) two places where 

 such patches of developed dilatator muscle occur. The patches are not 

 large, as the muscle-fibres are soon lost, so that before the periphery ot 

 the sphincter is reached all smooth muscle has disappeared, and thus the 

 dilatator has completely vanished. In the first general preparations that 

 I made, and which I stained in the usual way with Böhmer's hæmatoxylin- 

 eosin or according to van Gieson's method, the nature of these patches 

 was not clear to me, as it was not always possible to stain the muscle 

 distinctly; but after I had begun to stain à la Heidenhain, there was no 

 doubt about their being small bundless of plain muscle that lay just in front 

 of the epithelium. Fig. 9 shows, however, that sections stained by van 

 Gieson's method can also give clear, characteristic results 



In those places where the dilatator has developed, several types of it 

 may be found. Behind the sphincter, for instance, the normal conditions 

 are seen. I cannot say, in any case, that I have found any difference 

 between my series and my control preparations of this region. The types 

 that I have found also correspond well with the illustrations with which 



