CYCLOHA IN THE HUMAN KM15KYO. 



BY FRANKLIN P. MALL. 



The progress made in recent years on the study of teratology has been so 

 marked that it is now possible to reconsider the whole subject and to place it 

 upon a permanent scientific basis. For this progress we are indebted almost 

 exclusively to the experimental embryologists. Problems which formerly seemed 

 impossible of solution for example, the formation of the double monsters have 

 yielded as by magic to the embryologist, who made experimental studies upon 

 the living egg. Perhaps the best example that can be brought forward to illustrate 

 this point is the question of the cause of cyclopia. As soon as it was possible to 

 experiment on eggs in such a way that practically all of them developed into 

 cyclopean monsters the explanation of this condition was at hand. For this work 

 we are indebted entirely to Stockard. 



Before reviewing the four specimens which I have to report it may be well 

 to give an account of the theories regarding the origin of the cyclopean condition. 

 There are two chief theories, both resting upon an embryological basis. The 

 first of these is that the eggs begin to develop normally and that subsequently, on 

 account of an imperfect development of the head, the eyes coalesce to form a single 

 eye. This theory can be traced back to Meckel. The second is that the eyes 

 arise normally from the midventral line of the brain as a single structure, which 

 in the course of development divides into two eyes. This view was first advanced 

 by Huschke, who believed cyclopia to be due to an arrest of the development of 

 the brain at the time the eyes are forming. Although Huschke's opinion seemed 

 to be quite sound at the time it was advanced, it did not attach itself firmly to 

 literature, nor could we well accept it at present as resting upon a sound embryo- 

 logical basis. The figures which he gives in illustration shows first an early stage 

 of development of the brain, with a marked forebrain, and then an embryo with 

 two eye-vesicles hanging to the forebrain. He apparently confounded the whole 

 forebrain with the eye primordium. 



Meckel's studies rest upon much sounder embryological and anatomical 

 evidence, and his views gradually made their way into the literature of teratology. 

 Until a decade ago it was practically impossible to find any description of cyclopia 

 in which Meckel's studies were not reflected in the background. According to 

 Ahlfeld, Meckel states that cyclopia is characterized by a coalescence of the eye- 

 balls as well as of the orbital cavities. In case the orbital cavities unite very 

 early in development they distend evenly in a lateral direction. The tissues 

 which normally separate these cavities are absent or are pushed aside. In fact, 

 the structures which give the frame to the nose are most rudimentary, or absent, 

 while the nose itself is represented as a membranous snout, varying in form and 

 located above the confluent eyes. The mouth is frequently involved in this type 



