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Very soon after the entrance of the ovum into the uterus, in the human subject, the outer surface of the chorion is found beset with fine processes, the so-called chorion villi, which give it a rough and shaggy appearance. a, chorion with villi. The villi are shown to be best developed in the part of the chorion to which the allantois is extending, this portion ultimately becomes the placenta. ; b, space between the two layers of the amnion; c, amniotic cavity; d, situation of the intestine, showing its connection with the umbilical vesicle; e, umbilical vesicle; f, situation of heart and vessels; g, allantois.

Chorion Villi

Very soon after the entrance of the ovum into the uterus, in the human subject, the outer surface of…

Sagittal section in the median line of the female pelvis.

female Pelvis

Sagittal section in the median line of the female pelvis.

Section of mucous membrane lining body of uterus (decidua vera); fourth month of pregnancy.

Mucous Membrane of Uterus in Fourth Month of Pregnancy

Section of mucous membrane lining body of uterus (decidua vera); fourth month of pregnancy.

Uterine mucous membrane with part of muscular tissue.

Uterine Mucous Membrane

Uterine mucous membrane with part of muscular tissue.

Diagram of an early stage of the formation of the human placenta. Labels: a, embryo; b, amnion; c, placental vessels; d, decidua reflexa; e, allantois; f, placental villi; g, mucous membrane.

Early Formation of the Placenta

Diagram of an early stage of the formation of the human placenta. Labels: a, embryo; b, amnion; c, placental…

In the embryo the place of fibrous tissues is at first occupied by a mass of roundish cells, derived from the mesoblast. These develop into a network of branched cells or into groups of fusiform cells. Shown is a portion of submucous tissue of a uterus during pregnancy. Labels: a, branched cells, more or less spindel-shaped; b, bundles of connective tissue.

Tissue Growth of the Uterus

In the embryo the place of fibrous tissues is at first occupied by a mass of roundish cells, derived…

Diagrammatic view of a vertical transverse section of the uterus at the seventh week of pregnancy. Labels: c, c', cavity of uterus, which becomes the cavity of the decidua, opening at c, the cornua, into the Fallopian tubes, and at c' into the cavity of the cervix, which is closed by a plug of mucus; dv, decidua vera; dr, decidua reflexa, with the sparser villi imbedded in its substance; ds, decidua serotina, involving the more developed chorionic villi of the commencing placenta. The fetus is seen lying in the amniotic sac; passing up from the umbilicus is seen the umbilical pedicle of the yolk sac, which lies in the cavity between the amnion and chorion.

Uterus at Seventh Week of Pregnancy

Diagrammatic view of a vertical transverse section of the uterus at the seventh week of pregnancy. Labels:…

Section of the lining membrane of a human uterus at the period of commencing pregnancy showing the arrangement and other peculiarities of the glands, d, with their orfices, a, on the internal surface of the organ.

Lining Membrane of the Uterus

Section of the lining membrane of a human uterus at the period of commencing pregnancy showing the arrangement…