8 CYCLOPIA IN THE HUMAN EMBRYO. 



of monster and is usually rudimentary, while in some instances it, as well as the 

 snout, is missing altogether. Since the eyeballs are developed from pouches 

 which arise from the forebrain, it follows that the primary cause of this anomaly 

 is not to be sought in the development of the skull, but in the development of the 

 brain itself. We find in these cases that the width of the forebrain and midbrain 

 diminishes in the course of their development, corresponding to the union of the 

 orbital cavities and the eyeballs, making the brain appear at term much like that 

 of an embryo of the twelfth week. In addition to the atrophy of these parts, the 

 formation of the hemispheres as a single body is especially noticeable that is, they 

 have not been divided into two lobes. This division often is only slightly indicated. 

 The ventricles have united to form a single large cavity. In most of the cases at 

 birth the quantity of fluid within the ventricle is increased, so that as a rule we 

 have a large, bladder-like body in place of the forebrain. In this way is the fact 

 explained that in spite of the rudimentary development of the brain there is no 

 diminution of the size of the fore part of the head, as most cases of cyclopia are 

 accompanied with hydrocephalus. There are cases, however, in which there is 

 no hydrocephalus, which naturally result in a small head. This is most pronounced 

 in cases of cyclopia in double monsters in which the head contains two brains. 

 In these cases a symmetrical development of the brain is very rarely found. The 

 rudimentary brain can no doubt be held responsible for the most pronounced 

 specimens of cyclopean faces. In may be taken for granted that the nerves which 

 are to supply the deformed eye and face are simple in their development, cor- 

 responding in amount with the degree of the anomaly. 



This general description of the anatomy of the eye and face in cases of cyclopia 

 is one which will be found in most teratologies, and in all of these accounts it would 

 appear as though the authors mean to say that the eyes must arise from the fore- 

 brain and that they subsequently unite into a single compound eye, more or less 

 hourglass-shaped, due to an arrest of the growth of the brain which in some way 

 interfered with the development of the forehead and eventually left the nose 

 above the cyclopean eye. Teratologists are inclined to believe that the accom- 

 panying hydrocephalus is to be viewed as the primary cause of the anomaly, 

 although in many instances they try to trace this back to amniotic bands, which, 

 however, are not found in human specimens of cyclopia, and of course such bands 

 could play no role in the formation of this anomaly in animals which develop 

 without an amnion. Furthermore, the explanation of the formation of monsters 

 by means of amniotic bands is alluded to in recent teratologies only as one of the 

 myths of teratology. 



In my paper on monsters some ten years ago I gave a review of the experi- 

 mental work upon cyclopia as it appeared at that time. These statements I shall 

 recapitulate in part in order to bring out more clearly the recent progress made 

 in the study of cyclopia. 



In numerous experiments upon frog's eggs, Born, in 1897, occasionally pro- 

 duced monsters by splitting the head through its sagittal midplane after the 

 medullary plate was formed, and then readjusting the two halves. The pieces 



