l8 s. MÜLTII AND O. liEKNKK. M.-N. Kl 



versely). In other words, I have found the same strengthening bands that 

 Hekkfordt, Grynfelit and Forsmark describe and figure, the only diffe- 

 rence being that they are very rare in my material. It is also due to 

 the poor development of the dilatator that on the back of the iris, under 

 the microscope — preferably binocular — and a bright light, only very 

 few of the radial folds are visible, which with the same light and magni- 

 fying power, are seen in great numbers and density upon the back of the 

 )i()rnial human iris (PI. 14, fig. 15). 



With regard to the folds found on the back of the iris it should be 

 observed that they are more or less marked in the eyes of various animals. 

 No plausible explanation of them was given before the Danish investigator, 

 Heerfordt, propounded his theory that the dilatator is built up of muscle- 

 epithelium cells. When a muscle such as this, which is always found to 

 consist only of a single cell-layer, is to be increased, nature has two ways 

 of doing it. One of these is that the organ folds itself and thereby 

 provides a larger surface over which the muscle elements can spread; the 

 other way is for the cell-layer to project into the stroma in the form of 

 fillets. 



The existence of these folds has long been known, as they were 

 described by Schwalbe, In contrast to the short radial folds formed on 

 the posterior surface of the iris near the pupil by the contraction of the 

 latter, and therefore called by Schwalbe "contraction-folds", the same writer 

 gave to the peripheral long radial folds on the posterior surface of the 

 iris the name of "structural folds". 



Heerfordt, through his investigations of the developmental stages of 

 the dilatator in various animals, arrived at the conclusion that if the folding 

 does not provide sufficient additional surface for the increase of the bulk 

 of the dilatator, fillets form which penetrate more or less deeply into 

 the stroma. This is the case with the dilatator pupillae of the seal and 

 the otter, and both these animals need a very strong dilatator. Heerfordt 

 has carefully studied these fillets in the seal, and has found that they even 

 branched as they advanced into the stroma. Some of them were tubular, 

 and they were sometimes constricted oft' from the rest of the dilatator, 



Heerfordt uses only the expression "strengthening folds", and under 

 this designation describes both the folding of the posterior surface of the 

 iris and the fillet-like projections into the stroma. In man he has seen only- 

 very slight indications of such fillets. 



Forsmark, on the other hand, describes, under the name of "strength- 

 ening fillets", some more or less wide thickenings of the dilatator without 

 any trace of abnormal fold-formation at the place in question. His strength- 



