354 



HUM Atf UTERUS AND FETAL APPENDAGES. 



is probably degenerated epithelium. The decidua serotina is plainly divided into 

 an -upper compact, D', and a lower cavernous layer, D". The section figured 

 passes through an arterial vessel, Ve, which makes an abrupt turn so as to dis- 

 charge its blood into the intervillous spaces. 



The histological structure of all the parts should be carefully studied. (As 

 regards the structure of the amnion, see page 370.) 



The chorion consists of two layers, the outer ectodermic and inner mesodermic. 

 Over the chorionic membrane proper the ectoderm offers a great variety of appear- 

 ances. In some places it may be seen to have still its primitive organization, a 

 single inner layer of distinct cells and an outer syncytial layer, more or less similar 



Am. 



- J'TTTJ; * -- : rV' 3' < fcv'- v *~ ^^ v 31 C *""'! '" ** 



___-' -* .-- s -^ <3--<:r~*&>* -...,-*..,. ^-, *>v. ^-V...^.^--^""" 1 



"** " " ** "" -* M "* : '- - ''"' " ' :'-*-; ".-'' J - ' "' * "* ~' --- 



ZFib- 



FIG.- 235. HUMAN PLACENTAL CHORION AND AMNION OF THE FIFTH MONTH. 



Ep, Amniotic epithelium. Am, Amnion. Str, Stroma. Fib, Fibrillar layer. Fbr, Fibrin layer, c, Chorionic 

 cellular layer of ectoderm. Vi, Chorionic villi. X 71 diams. 



to those represented in figure 243. For the most part, however, the chorionic ecto- 

 derm has been considerably modified from its primitive condition. The inner or 

 cellular layer exhibits irregular, thickened patches, which present every possible 

 degree of variation as to their size. A cell patch from a somewhat younger stage 

 is represented in figure 235 as seen with a low magnification, and another patch 

 of the age we are studying is represented in figure 236. The patches vary in 

 appearance; the cells are more distinct in the small patches, less so in the large 

 patches, in which there are often parts more or less degenerated. The cell-bodies 

 stain lightly; their nuclei are granular, not very sharply defined, and variable in 

 size and shape. The cellular layer is always sharply defined against the mesoderm. 

 Toward the outside the patches offer varying relations. In some cases a part of 



