110 On Heterochromia Iridis in Man and Animals 



Distribution of the Spot and Ray Patterns on the Iris. 



Spotted Pattern : 



In both eyes 7 



{Above the horizontal equator 5 



On the horizontal equator ... 4 



Above and below equator ... 4 



Below equator... ... ... 18 



Distribution of the Ray : 



Single Eay above equator ... 2 



on „ ... 2 



,, below „ ... 18 



Multiple rays above and below 11 



Total 33 



18 below it in various positions in the lower half of the iris. In the 

 11 cases in which a large portion of iris surface was covered by multiple 

 duplex rays the greater number and wider and more deeply pigmented 

 rays occurred in the lower half of the iris. 



This inferior situation of the duplex ray is suggestive when we 

 recall the fact that congenital coloboma of the iris, which is often 

 bi-lateral and which is probably dependent on imperfect closure of the 

 choroidal fissure, is nearly always found in the lower half of the iris and 

 usually in the downward vertical direction. The occurrence of coloboma 

 of the iris has been recorded in the upper portions of the iris, and an 

 attempt to explain this fact has been made by supposing that in these 

 cases some rotation of the developing optic cup has carried the choroidal 

 fissure out of its usual inferior position. It is also interesting to note 

 that in some of the amphibia (frog and toad and some newts) a colour 

 coloboma of the margin of the iris in the vertically downward direction 

 normally exists in the adult animal. Plate VII, fig. 3. 



The fact that while coloboma is nearly always vertically downwards 

 the pigmented ray is rarely in the exact vertical midline but usually 

 displaced to one or other side of the lower half of the iris, would at first 

 suggest a dififerent origin for the abnormality in the two cases. 



But it is necessary to remember that coloboma is due to non-closure 

 of a gap which nearly always forms in the same position, while the ray 

 of pigment is the result of the in-growth of mesoblastic tissue which 

 eventually becomes pigmented through this choroidal fissure, and the 

 spreading out round the globe of this tissue in a radial or fan-shaped 

 manner, to form the iris etioma. The habitual presence of the pig- 

 mented rays in the lower half of the iris may be due therefore to the 



