346 HUMAN UTERUS AND FETAL APPENDAGES. 



spongy mass soaked with maternal blood. This mass consists of numerous trees of 

 tissue, which spring with comparatively thick stems from the chorion and branch 

 again' and again. In these stems and branches are to be found the final ramifica- 

 tions of the vessels of the umbilical cord; the trees are known as chorionic or 

 placental mill. Some of their end-twigs are very closely attached to the surface of 

 the decidua. In the center of the placental area the villi form a mass about three 

 fourths of an inch thick, but toward the edge of the area the mass gradually thins' 

 out until at the very edge the chorion and decidua come into immediate contact. 

 The mass of villi, together with the overlying portions of the chorionic and am- 

 niotic membranes and the underlying portion of the decidua, constitutes what is 

 known as the placenta. The decidua of the placental area is called the decidua 

 serotina; the chorion of the placenta is known as the chorion frondosum. When 

 birth takes place, the whole placenta is expelled after the delivery of the child; the 

 placenta of the obstetrician is, therefore, partly of fetal, partly of maternal, origin. 



Decidua Vera of the First Stage in Section. 



Specimens may be preserved in Zenker's or Tellyesnicky's fluid, or they may 

 be preserved with less good results in Miiller's or Parker's fluid or in picro-sulphuric 

 acid. Sections may be made of the, en tire wall in celloidin, or, if it is desired to 

 get thinner sections, in paraffin, in which case it is advantageous to remove as 

 much as possible of the muscular coat so as to cut only the decidual membrane. 



The following description is based upon a uterus one month pregnant. Figure 

 228 was obtained from a vertical section of the decidua, by drawing the outlines 

 of the glands or gland spaces, Gl, and by dotting the entire area occupied 

 by the connective tissue. The blood-vessels are indicated by double outlines. 

 The artery, Art, owing to its spiral course, is cut repeatedly. The figure 

 demonstrates very clearly that the gland cavities are so arranged that the decidua 

 is divided into an upper compact layer, Comp, and a lower cavernous layer, 

 Cav, the difference being due to the size and number of the gland cavities. The 

 amount of epithelium to be observed at this stage varies greatly. It is sometimes 

 wholly absent from the surface, in other cases absent or present in patches. In the 

 glands the epithelium has. undergone many modifications. In some parts the original 

 cylinder epithelium of the glands is well preserved in patches, and such patches 

 of epithelium are found at every stage- until after delivery. It has been observed 

 that these patches serve to regenerate the epithelium of the glands, and, by spreading 

 from the glands on to the surface, to regenerate also the epithelial covering of the 

 uterine mucosa. But for the most part the glandular epithelium is considerably 

 altered. We find places in which the cells, though attached to the surrounding 

 connective tissue, are separated from one another by small fissures. In other places 

 the cells are a little larger (Fig. 229), each for the most part cleft from its fellow, 

 and some of them loosened from the wall and lying free in the cavity. Apparently 

 the cells' which are thus freed become swollen, probably by imbibition, both the 



