A system of obstetrics . yer, [mmediately external to the amniotic layer comes the chorion (ch),from whose outer surface the very numerous, greatly-branched, tortuousvilli (v) project: these villi soon lose their proper epithelium derivedfrom the subzonal membrane (p. 132); the structure of their terminalbranches has been shown in G, Fig. 62. The allantoic arteries reach-ing the chorionic layer through the umbilical cord (/) ramify in thislayer in the form of a number of large branches which spread overit just beneath the amnion: one of these branches is represented cutacross at vf. The termin
A system of obstetrics . yer, [mmediately external to the amniotic layer comes the chorion (ch),from whose outer surface the very numerous, greatly-branched, tortuousvilli (v) project: these villi soon lose their proper epithelium derivedfrom the subzonal membrane (p. 132); the structure of their terminalbranches has been shown in G, Fig. 62. The allantoic arteries reach-ing the chorionic layer through the umbilical cord (/) ramify in thislayer in the form of a number of large branches which spread overit just beneath the amnion: one of these branches is represented cutacross at vf. The terminal branches of the arteries when they have 138 DEVELOPMENT OF THE EMBRYO. become reduced to the size of a crowquill suddenly dip down from thesurface and enter the villous layer. The larger trunks also, as theydiverge, give off branches from their deeper sides which supply thevilli. The veins, returning the foetal blood, have a course similar tothe arteries: the larger trunks converge toward the funis, and there Fig. (From Allen Thomson.) Diagrammatic Representation of a Section of the Human Placenta,near the margin, at five or six months: am. amnion; ch, chorion : from its under surfacethe branched villi are seen to project; m, muscular coat of uterus with divided blood-ves-sels; v, decidua vera; r, decidua reflexa; s, placental serotina; s, uterine serotina; ds, septaof placental serotina separating the lobes of the placenta: near their bases are seen thecoiled arteries; cs, circular sinus, a great vein which runs around the margin of the pla-centa. enter the umbilical (allantoic) In the villi the arteries and veinsare connected by a capillary network. The amniotic layer and the chorionic layer, with the villi and blood-vessels of the latter, constitute the foetal portion of the placenta. Soon after the chorion frondosum comes in contact with the deciduaserotina the inner stratum of the latter becomes greatly modified. Itloses its lining epithelium, and the superf
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectobstetrics, bookyear1
