16 CYCLOPIA IN THE HUMAN EMBRYO. 



The two halves of the chorion having been cut into serial sections, it was possi- 

 ble to ascertain with greater precision the attachment of the umbilical cord as well 

 as the amniotic adhesions spoken of above. It was found that the cord was 

 attached to one half and that there were delicate amniotic adhesions in the other 

 half of the specimen. The attachment of the cord was by means of blood-vessels 

 passing directly from the embryo to the chorion, while the adhesions in the second 

 half were by means of loose strands of mesenchyme cells binding the amnion to 

 the chorion. 



The tissue of the chorion appears much like that in normal ova. It is of 

 about the same quantity and is possibly a little more fibrous. The mesenchyme 

 of the villa is well infiltrated with embryonal blood-cells, and their trophoblast 

 is quite scanty. At points the villi are stuck together with maternal blood, in 

 which are found islands of syncytial cells, showing that the infiltration of blood 

 took place before the time of the abortion. The mesenchyme of a few of the villi 

 takes on an intense hematoxylin stain, which indicates that it is degenerating. 

 In fact, the cells of the mesenchyme in many of the villi have mostly disintegrated. 



The reticular magma stains intensely with eosin. Scattered through the 

 dense network composing it are numerous large protoplasmic cells containing nuclei. 

 In certain places the cells accumulate in large masses, forming colonies. No doubt 

 these are the so-called Hofbauer cells, so well described by Essick. 



The embryo had been cut into a very perfect series of transverse sections, 

 which show that very little unequal shrinkage took place while it was being 

 embedded. Nearly the entire wall of the central nervous system is in apposition 

 with the surrounding mesenchyme. However, there are occasional separations 

 along the dorsal midline in the head region, the most pronounced one being around 

 the midbrain, but this is not marked. The thin roof-plate of the hindbrain has 

 collapsed only to a slight extent. All in all, the preservation, embedding, mount- 

 ing, and staining of this specimen is quite perfect. 



There are numerous cell divisions in the brain-tube around the central canal 

 as well as in the retina of the cyclopean eye. Furthermore, these cell divisions are 

 found also in the atrophic cerebral vesicle, showing that at the time of the abortion 

 the atrophic cerebral vesicle, as well as the cyclopean eye, was growing actively. 



The form of the head is well shown in the figures. In order to study the head 

 with greater care a model was made of the external form at a scale of 50 diameters. 

 This model shows the shrinkage of the head while the specimen was being embedded. 

 It was made so that the entire head could be removed from the body in order to 

 give a face view of the embryo, which could not be obtained from the specimen 

 before it was cut into sections (plate 1, fig. 3). The model also shows the mid- 

 brain to be very prominent, the frontal process being pronounced but small. The 

 eyes are shown deep in the head, and the snout protrudes above the mouth from 

 a point immediately below the process and just in front of the eye. The body 

 otherwise appears to be normal in form, and a microscopic survey of the sections 

 shows that the tissues are also normal in structure. 



