350 HUMAN UTERUS AND FETAL APPENDAGES. 



more developed upon the inner or chorionic side than upon the outer side of the 

 reflexa. On the inner side it forms a dense network, which fuses with the degen- 

 erated ectoderm of the chorionic villi wherever the villi are in contact with the de- 

 cidua. It also ramifies nearly halfway through the decidua, the ramifications being 

 followed easily, owing to the dark staining of the substance. Over the outside of the 

 decidua the fibrin forms a much thinner layer or may be only indistinctly formed. 



In a decidua reflexa of three months the conditions are essentially the same, 

 except that the degeneration is further advanced and the membrane thinner. 

 Traces of cellular structure are still more vague and the fibrin is more developed. 

 In all parts of the membrane there appear leucocytes which are particularly 

 numerous and conspicuous in the neighborhood of the placenta. It is natural to 

 assume that they are concerned in the resorption of the reflexa. There is an inner 

 thicker layer of fibrin and a thinner outer layer, which is now always present and 

 distinct. Between these two layers is a stratum in which the remains of the cells 

 may be seen. Occasionally there is an appearance which suggests surviving de- 

 cidual cells, and, indeed, in sections taken from parts close to the placenta true 

 decidual cells may be identified. 



The origin of the chorion laeve by the disappearance of its villi is described 

 on page 367. The sections of the decidua reflexa will enable the student to see 

 also some of the phases of the degeneration of the villi. They are very much 

 altered. Their ectoderm undergoes a hypertrophic degeneration and becomes hya- 

 line tissue, which stains darkly. The degenerated ectoderm of adjacent villi fuses 

 more or less extensively. The mesoderm of the villi shows a partial loss of its 

 primitive cellular organization. 



Decidua Vera and Chorion Laeve of the Second Stage. 



Pieces of the decidua vera of from six to nine months with the chorion and 

 amnion carefully preserved in situ may be hardened in Miiller's or Tellyesnicky's 

 fluid. Blocks half an inch or less in size may be imbedded in celloidin, and sec- 

 tions made perpendicularly to the surface may be stained with alum hematoxylin 

 and eosin, or with Heidenhain's hematoxylin and orange G, or with picro-carmine. 



The decidua reflexa having been resorbed, the chorion (Fig. 233, Cho) has 

 come into contact with the surface of the uterus, and the chorionic epithelium, c, 

 is closely adherent to the surface of the decidua, from which the original epithe- 

 lium has completely disappeared. The amnion is loosely connected with the 

 chorion by a few strands or threads, which are represented in the figure and the 

 nature of which is not known. Both the amnion. Am, and the chorion, Cho, 

 being developed from the original somatopleure (compare page 82), consist of a 

 mesodermic and an ectodermal layer. The ectoderm of the amnion is a single 

 layer of cuboidal cells placed on the side of the membrane toward the embryo and 

 away from the uterus. The ectoderm, c, of the chorion, on the contrary, is next 

 the uterus. Hence it will be noticed that the mesodermic layers of the amnion 



