. Cunningham's Text-book of anatomy. Anatomy. 60 HUMAN EMBEYOLOGY. the whole of the surface of the zygote, and thus, for a tune, the whole of the surface of the chorion is covered with villi. As the embryo grows, and the amnion and the extra-embryonic ccelom are distended, the zygote increases in size, and the capsular portion of the decidua is stretched till its vascular supply is interfered with and the villi associated with it undergo atrophy and disappear. When these degenerative changes have occurred, the portion of the chorion in association with the thinned decidua capsularis presents a
. Cunningham's Text-book of anatomy. Anatomy. 60 HUMAN EMBEYOLOGY. the whole of the surface of the zygote, and thus, for a tune, the whole of the surface of the chorion is covered with villi. As the embryo grows, and the amnion and the extra-embryonic ccelom are distended, the zygote increases in size, and the capsular portion of the decidua is stretched till its vascular supply is interfered with and the villi associated with it undergo atrophy and disappear. When these degenerative changes have occurred, the portion of the chorion in association with the thinned decidua capsularis presents a relatively smooth surface, and is known as the chorion laeve. Whilst the decidua capsularis is being stretched and thinned, and the associated portion of the chorion is being reduced to the condition of a non-villous region, the decidua basalis increases in thickness ; at the same time the villi associated with it increase in size and in the complexity of their branches. The portion of the chorion from which these large villi spring is termed the chorion frondosum. It is this portion of the chorion which takes Placental area Intervillous space Spongy lay Umbilical cord Muscular wall of uterus ''Amnion cavity Uterine tube _ Vitello- intestinal duct. Compact layer of decidua Troplioblast Fused mesoderm of chorion and amnion Ectoderm of amnion .Spongy layer Chonse - Rectum »-^| Small intestine ,• Amnion cavity Trachea Pericardium Fig. 78.—Schema of a Section of a Pregnant Uterus after Fusion of Amnion and Chorion. part in the formation of the so-called foetal portion of the placenta, the maternal part of that organ being formed by the decidua basilis. The placenta, therefore, is formed partly by the zygote and partly by maternal tissues, but the interchanges between the foetal and the maternal blood take place in the tissue of the zygote through the troplioblast which covers the surfaces of the villi. As the growth of the embryo and the distension of the amnion continue, the
Size: 1454px × 1718px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1914
