346 HUMAN UTERUS AND FCETAL APPENDAGES. 



the glands of the uterus at any period, as was at one time supposed. The ecto- 

 derm on the tip of the villi, where it is in contact with decidual tissue, undergoes 

 a hyaline degeneration. 



The shape of the mlli varies according to the part of the chorion and the age 

 of the embryo. Over the chorion laeve there is first an arrest of development and 

 a subsequent slow degeneration of the tissues, which lose all recognizable organ- 

 ization of their protoplasm, and to a large extent of their nuclei also. At the 

 same time they alter their shape (Fig. 200), becoming more and more filamen- 

 tous. By the fourth month only a few tapering threads with very few branches 

 remain. The villi disappear almost completely from the chorion laeve, except 

 near the edge of the placenta. The mlli of the chorion frondosum or placental 



x9 



FIG. 200. ABORTING VILLUS FROM THE HUMAN FIG. 201. FRAGMENT OF THE CHORION OF FIG. 



CHORION IVEVE OF THE SECOND MONTH. 69, HIGHLY MAGNIFIED. 



EC, Ectoderm. Mes, Mesoderm. Vi, Villus formed 

 wholly by ectoderm. 



region, on the contrary, make an enormous growth. At first they are short, 

 thick-set bodies of irregular shape, as shown in figure 201. At twelve weeks 

 their form is extremely characteristic (Fig. 202). The main stem gives off 

 numerous branches at more or less acute angles, and these again other branches, 

 until at last the terminal twigs are reached. The branches are extremely irregu- 

 lar and variable, though in general club-shaped and constricted at the base. The 

 branches may be bigger than the trunk which bears them, or of any less size. In 

 older stages there is a progressive change. During the fifth month we find the 

 irregularity of shape, though still very marked, decidedly less exaggerated (Fig. 

 203). The branches tend to come off at more nearly right angles. One finds 

 very numerous free ends, as of course only a small portion of the branches touch 



