THE UMBILICAL CORD. 



351 



though always far less so than the nuclei of the mesenchyma of the embryo 

 proper. In other cases (Fig. 210) the nuclei are exceedingly irregular; some 

 are large with a distinct network, d; others are smaller and differ but slightly 

 from the normal. Some are very irregular, 6, others slightly irregular, c, and 

 others again strangely elongated and narrow, a. Many other forms besides 

 those represented in figure 210 may be found. It has been suggested that these 





Fig. 210. — Natural Group of Nuclei from the Mesoderm of the Human Amnion of the Fifth 

 Month. (For lettering see text.) X 1225 diams. 



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, for 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 best preserved in Zenker's or Tellyesnicky's 

 fluid. Transverse sections may be prepared in paraffin and stained with alum 

 hematoxylin and eosin, or with Heidenhain's iron hematoxylin and orange G; 

 or, if it is desired to study the development of the connective-tissue fibrilla, with 

 Mallory's triple connective-tissue stain. 



A general description of the umbilical cord has been given, pages 109 to 

 III, and there two sections (Fig. 51) are represented showing the structures 

 which appear in sections of the umbilical cord. At full term some of these 

 structures are still present but somewhat modified (Fig. 211), while others have 

 been partly or wholly obliterated. As contrasted with the early stages, we find 



