372 



HUMAN UTERUS AND FETAL APPENDAGES. 



a layer of nearly homogeneous basal substance or matrix immediately underneath 

 the ectoderm and remarkable for containing no cells. Sometimes the remaining 

 portion of the mesoderm is broken up so as to offer a fibrillar structure (Fig. 252, 

 A), and when that is the case we can no longer make out a distinct mesothelial 

 layer. At other times the more or less homogeneous matrix can be seen through 

 the whole thickness of the amnion (Fig. 252, B), and when this is the case the 

 mesothelium, a, can be readily identified. 



In surface views the amniotic ectoderm is seen to consist of more or less 

 regularly distributed nuclei with cell-bodies connecting with one another by inter- 

 cellular bridges of protoplasm (Fig. 253). The nuclei, nu, are relatively large, 



rounded, and with distinct outlines. They 

 have a more or less well-marked intranuclear 

 network with thickened nodes and a small 

 number of deeply stained granules which 

 are probably chromatin. Each nucleus is 

 surrounded by a cell-body, pi, and the ad- 

 jacent cell-bodies are separated from one 

 another by clear spaces which are crossed 

 by threads of material, pr, stretching as 

 bridges between the neighboring cells. The 

 protoplasm is vacuolated. The whole picture 

 thus leads to the view that the epithelium 

 is a sponge-work of protoplasm somewhat 

 condensed around each nucleus. As re- 

 gards the mesoderm, it is very difficult to 

 obtain clear pictures of the cells, though 

 the nuclei can be readily observed. They vary greatly in appearance, being some- 

 times fairly regular and uniform, though always far less so than the nuclei of the 

 mesenchyma of the embryo proper. In other cases (Fig. 254) the nuclei are exceed- 

 ingly irregular; some are large with a distinct network, d; others are smaller and 

 differ but slightly from the normal. Some are very irregular, b, others slightly 

 irregular, c, and others again strangely elongated and narrow, a. Many other 

 forms besides those represented in figure 254 may be found. It has been sug- 

 gested that these varied shapes of the nuclei indicate degenerative changes, and, in 

 fact, many of the nuclei are actually breaking down, for in some specimens every 

 stage between a nucleus and scattered granules can be observed, and one may find 

 nuclei with distinct membranes, without membranes, masses of granular matter stained, 

 clusters of granules crowded together, and, finally, other clusters more or less scattered. 



The Umbilical Cord. 



The umbilical cord may be well preserved in Zenker's or Tellyesnicky's fluid. 

 Transverse sections may be prepared in paraffin and stained with alum hematoxylin 



FIG. 254. NATURAL GROUP or NUCLEI FROM THE 

 MESODERM OF THE HUMAN AMNION OF THE 

 FIFTH MONTH. (For lettering see text.) 

 X 1225 diams. 



