. Cunningham's Text-book of anatomy. Anatomy. THE PLACENTA. 59 by a layer of cellular trophoblast, Langhan's layer, which lies next the mesoderm, and a layer of Plasmodium external to the cellular layer. The proximal end of .each villus is continuous with the chorion plate of the intervillous spaces, formed by the chorion, and the distal extremity is connected by the plasmodial basal layer of the trophoblast, which forms the outer boundary of the intervillous spaces and which is fused with the maternal decidual tissue. After a time branches are projected from the sides of the secondary villi i

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. Cunningham's Text-book of anatomy. Anatomy. THE PLACENTA. 59 by a layer of cellular trophoblast, Langhan's layer, which lies next the mesoderm, and a layer of Plasmodium external to the cellular layer. The proximal end of .each villus is continuous with the chorion plate of the intervillous spaces, formed by the chorion, and the distal extremity is connected by the plasmodial basal layer of the trophoblast, which forms the outer boundary of the intervillous spaces and which is fused with the maternal decidual tissue. After a time branches are projected from the sides of the secondary villi i
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Image ID: PFYCN0
. Cunningham's Text-book of anatomy. Anatomy. THE PLACENTA. 59 by a layer of cellular trophoblast, Langhan's layer, which lies next the mesoderm, and a layer of Plasmodium external to the cellular layer. The proximal end of .each villus is continuous with the chorion plate of the intervillous spaces, formed by the chorion, and the distal extremity is connected by the plasmodial basal layer of the trophoblast, which forms the outer boundary of the intervillous spaces and which is fused with the maternal decidual tissue. After a time branches are projected from the sides of the secondary villi into the intervillous spaces. In this way two sets of secondary villi are differentiated, (1) the anchoring villi (Fig. 79), which cross from the chorion to the Intervillous space Secondary villus Anchoring villus Maternal rtery Umbilical cord -~ Decidua Temporarily herniated smal' intestine Decidua capsular! Trophoblast o chorion lsevi. terine tube Unchanged part of uterine gland ilated part of terine gland ecidua capsulans —Trophoblast Mesoderm lining of chorion laeve -^Mesoderm of amnion Pancreas"' Amnion cavity Ectoderm of amnion Decidua vera pericardium (heart not shown) Fig. 77.—Schema of a Section of a Pregnant Uterus after the Formation of the Umbilical Cord. Note that the expanding amnion has almost obliterated the extra-embryonic ccelom which lies between it and the chorion. basal layer of trophoblast and are attached to the latter by cell columns, which are the remains of the primary villi which have not been penetrated by the foetal mesoderm, and (2) free or absorbing villi (Fig. 76), which extend from the sides of the original secondary villi into the blood, in the intervillous spaces. Whilst the trophoblastic invasion of the compact layer of the decidua is proceeding, not only are the interglandular elements of the decidua destroyed, but the walls of the glands also, and, as a consequence, some of the glands in the decidua basalis open for a time into the

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