1922. No. 4. MIOSIS CONGENITA SEU MICROCORIA FAMILIARIS. I7 



the various writers on this subject have furnished their works. In my 

 fig. 10 I have shown a piece of dilatator behind the sphincter, and it will 

 there be seen that in front of the nuclear part of the niuscle-epithelium 

 quite large amounts of contractile elements are gathered. 



In those regions in which the dilatator is more or less poorly deve- 

 loped, various conditions are represented. If we follow the development 

 from the complete absence of the muscle as I have shown it in fig. 9, we 

 see, as shown in fig. 11. that in front of the unditîerentiated front layer 

 of epithelium — i e., that which should have become muscle-epithelium, 

 but has been hindered in its development, and therefore appears onlv in 

 the form of spindle-shaped epithelial cells — there lies a single slender 

 cell between the epithelium and the stroma. In form this cell (shown in 

 fig. Ill resembles a plain-muscle cell, but I have not found myoglia fibres 

 de\-eloped in it, and it should probably be regarded as an intermediate 

 stage between an epithelium cell and a plain-muscle cell. In most cases, 

 however, there are myoglia fibres in these spindle-shaped cells, and there 

 is therefore no reason to doubt that these are cells of plain muscle lying 

 in front of the layer of epithelium Three or four such muscle cells are 

 not infrequently seen lying one in front of another so as to form a thick 

 layer of unstriped muscle at that place. As fig. 1 1 shows, we find in 

 these cells the long, thin, rod-like nucleus that is so characteristic of the 

 ordinary mesodermal muscle, whereas all writers appear to agree that the 

 cells of the dilatator pupillae are characterised, inter alia, by their more 

 oval, and in any case not rod-shaped, nuclei. Figs. 7 and 9, together with 

 fig. II, give a good general idea of the form of the cell and of the nucleus. 

 These figures are taken from various sections of various regions. It will 

 be seen how the muscle epithelium in fig. 7 consists of blunt-pointed cells 

 which in fig. 9 are elongated and have assumed more the shape of the 

 plain-muscle cell, and finally, in fig. 11. appear as cells with almost all the 

 properties of the plain-muscle cell. In transverse sections is seen a layer, 

 more or less thin according to the degree of development of the contractile 

 elements, of transversely cut fibrils in front of the epithelium. Fig, 12 

 seems to me to be a good illustration of this, as it shows how the muscle 

 fibrils become fewer from left to right. It also shows that the epithelium 

 cells are not always uniform, and that here and there, at any rate, there 

 may be more than 2 rows of cells in the epithelium. 



In some places, especially near the ciliary body, many such plain- 

 muscle cells may be found, as I have said, in front of the epithelium, 

 and in a few places there are so many that they form a projecting fillet, 

 which extends far into the stroma (see fig. 13, where they are cut trans- 



Vid.-Selsk. Skrifter. I. M.-N. Kl. 1922. No. 4 2 



