892 



SPERM, OVA, AND PREGNANCY 



rion (Fig. 15.1). However, on one side, 

 where the thick, well vascularized endo- 

 metrium favors their growth, the villi be- 

 come long, branched, and profuse, forming 

 the chorion frondosum which eventually 

 gives rise to the definitive, discoidal pla- 

 centa. 



As the trophoblast invades the endome- 

 trium giving rise to the placental villi, di- 

 lated endometrial blood vessels are eroded 

 and tapped, their contents providing nour- 

 ishment for the proliferating blastocyst. The 

 maternal blood lacunae become increasingly 

 confluent, forming a more or less continuous 

 intervillous space between the placental 

 villi. This space acquires afferent and effer- 

 ent connections with the arteries and veins 

 of the uterine wall, as a consequence of 

 which maternal blood begins to circulate in 

 the intervillous space and to bathe the sur- 

 face of the villi. In the mesodermal stroma 

 of the placental villi, newly formed blood 

 vessels become connected with the blood 

 vessels and developing heart within the 

 growing embryo, so that toward the end of 

 the first month, fetal blood begins to cir- 

 culate in the capillaries of the villi. The 

 secondary and tertiary villi continue to 

 lengthen and branch. A number of large 

 stem or anchoring villi extend across the 

 intervillous space to attach to the tropho- 



blastic shell or basal plate which is apposed 

 to the uterine decidua. 



As the blastocyst grows, the endome- 

 trium surrounding it undergoes significant 

 changes. The zone in which the trophoblas- 

 tic shell and the endometrium meet has been 

 variously called the "junctional," "com- 

 posite," or "penetration" zone. The endo- 

 metrium subjacent to the junctional zone 

 comprises an outer cellular portion, the 

 stratum compactum and a deeper glandular 

 part, the stratum spongiosum, the latter 

 characterized by the presence of conspicu- 

 ous, actively secreting glands. The spongy 

 layer extends down to the basal zone, the 

 latter forming a narrow strip which is con- 

 tiguous to the myometrium and contains the 

 fundic ends of the uterine glands. The 

 stromal cells of the compact zone and, 

 later, of the glandular zone, become trans- 

 formed into large polygonal elements termed 

 decidual cells. This decidual transformation 

 occurs throughout the entire extent of the 

 endometrium. That portion of the decidua 

 directly beneath the implanted blastocyst 

 constitutes the maternal part of the pla- 

 centa and is called the decidua basalis. It 

 is attacked and resorbed to a large degree 

 by the growing placenta. Its remnants, at 

 the time of birth, are either expelled or un- 

 dergo resorption. The endometrium renews 



Plate 15. IV 



All of the figures (excepting Fig. 15.13) on this plate are drawings of frozen sections of ma- 

 terial fixed in 10 per cent buffered formalin. 



Fig. 15.13. The trophoblast of a human chorionic villus of 30 days. Stained with osmic acid 

 by Champy's fixation, a procedure which differentiates lipids. The syncytium contains nu- 

 merous fat droplets, whereas the Langhans cells contain none. In the stroma beneath the 

 trophoblast a typical, vacuolated Hofbauer cell is visible. These fat droplets are similarly re- 

 vealed after staining with sudan dyes. X 1600. (Wislocki and Bennett, 1943.) 



Fig. 15.14. Human placental villus at full term stained with sudan black B showing minute 

 lipid droplets in the syncytium. Some villi contain more lipid particles than this one. X 7 

 ocular; X 60 objective. Compare Figures 15.13 and 15.14 wdth Figures 15.18 and 15.19, the 

 latter stained by the Ashbel-Seligman carbonyl method. 



Fig. 15.15. Placenta of a pig (fetal crown to rump length, 120 mm.), showing the chorion 

 in apposition to the endometrium. Sudan black B. The uterine epithelium contains numerous 

 black, sudanophilic droplets whereas none are visible in the faintly gray staining tropho- 

 blastic cells of the chorion. Compare with Figure 15.22, showing the Ashbel-Seligman car- 

 bonyl reaction which is identical in its distribution with the sudanophilia. X 10 ocular; X 20 

 objective. 



Fig. 15.16. The labyrinth of the chorio-allantoic placenta of a rat on the 18th day of gesta- 

 tion, showing numerous sudanophilic lipid droplets in the cytotrophoblasts. Compare with 

 Figure 15.21, showing the Ashbel-Seligman carbonyl reaction. 



Fig. 15.17. The labyrinth of the chorio-allantoic placenta of a mouse on the 18th day of 

 gestation stained by the Ashbel-Seligman carbonyl reaction. The placental labyrinths of 

 mouse and rat are identical in respect to their sudanophilia and carbonyl reactions. X 10 

 ocular; X 60 objective. 



