26 s. HOLIH A.NO O. I;EF<NH<. M.-N. Kl. 



behind the sphincter. The tube has therefore been produced by a du- 

 [iHcature of the layer of muscle epithelium. 



It is not always, however, that the sphincter has succeeded in drawing 

 a di\ erticulum such as this out of the dilatator. The long connecting fibres 

 are often seen attached to the dilatator without having any influence on 

 the course of that muscle. Fig. i8 shows how such a long, slender con- 

 necting fibre attaches itself to the dilatator without causing any change in 

 the direction of the epithelial layer. With regard to the attachment of the 

 connecting fibres it is worthy of notice that at such points a strengthening 

 of the dilatator layer always seems to have formed, as there are several 

 layers of smooth-muscle cells just wehere the attachment takes place. It 

 almost appears as if there had been a proliferation of the dilatator at 

 this point. 



Dr. Ilolth's clinical discoveries in the three cases may indicate that 

 the iris in all of them is of the same structure, or, in other words, that 

 dilatator is found developed behind the sphincter, while elsewhere it is 

 almost entirely absent. If this should prove to be the case in subsequent 

 examination of the eyes of other persons with this anomaly, there are 

 supports for the explanation of the circumstance in the embryology of the 

 sphincter. 



The rudiment of the sphincter appears much earlier than that of the 

 dilatator, namely, in the 4th month, while the dilatator appears in the 6^^ 

 month. The development of the sphincter, moreover, is not complete until 

 the 9^1^ month of fœtation. Throughout this long period the sphincter, 

 according to Herzog and Szily, is in close connection with the cells in 

 the front epithelial layer of the secondary optic cup, in other words to 

 those cells which subsequently developed into the pupillary part of the 

 dilatator. The connection is so close that Herzog, who has investigated 

 the conditions in mice and rats, could not distinguish the front layer of 

 epithelium from the rudiment of the sphincter; and Szily draws attention 

 to the lateness with which mesenchyma intrudes itself and separates the 

 two muscles. According to the last-named writer, the difterence between 

 the iris of the new-born child and that of the adult is that in the child 

 the sphincter lies in almost complete contact with the front layer of epithe- 

 lium in the pars iridica. "Die die scharfe Trennung bewerkstelligende 

 Bindegewebslage ist also in der Hauptsache eine erst nach der Geburt 

 erscheinende Bildung", he says. Herzog even found, in a 30 days old 

 rabbit, that the sphincter and the dilatator lay in direct contact with each 

 other. Forsmark has also found that the layer of muscle-epithelium in 



