The developmental features with the macroscopical changes on 1227 cases . of the placentas from the korean during the period from second lunar month(fifth week) until the full term of the gestation have been studied by weighing the placentas, measuring the long and short diameters, the thickness, the length of the umbilical cord, and observing the insertion sites of the umbilical cord on the fetal side of the placental surface, the shape of the placentas, the obliquity of the umbilical cord, in addition to the above by the calculating the placental coefficient.
These studies were further extended aver the quantitative histology on 81 out of 1227 cases of the placenta .by adopting the Chalkley´s analytical method;, the cellular components of the tissue and the size of cells of the placenta were involved.
From the above studies the following conclusions could be drawn:
1) The mean value of the long diameter of the placenta from the tenth lunar month of the gestation is 192.0 mm which is approximately 1.66 times longer than 115.5 mm from the fourth.
2) The mean value of the short diameter. of the placenta from the tenth lunar month of the gestation is 164.2 mm which is approximately 1.93 times longer than 85.0 mm from the fourth.
3) The mean value of the thickness of the placenta from the tenth is 22.6 mm which is approximately - 1.75 times larger than 12.9 mm from the fourth.
4) The mean value of the placental weight from the tenth is 447.4 gins which is corresponded to .6.23 times heavier than 71.8 gms from the fourth.
5) The mean value of the placental coefficient from the fourth is 0.86 which is very high, and is, however, decreased with time "until the tenth at 0.17 which is the lowest value. The mean value of the ratio of the fetus weight to the placental weight from the fourth is 1.2, and is increased with the time until the tenth at which the value is 5.9.
6) The commonest of all the placental shapes is the elliptical, and is followed by the nearly round one. The purely round in the shape is relatively rare. The shape of the placenta is not changed throughout the period of the gestation.
7) The commonest site of the insertion of the umbilical cord on the fetal placental surface is an excentral, and is followed by the central, while the peripheral and velamentous insertion of the cord are relatively rare 8) The mean value of the length of the umbilical cord, which is approximately corresponded to that of ´ the fetal body, from the tenth of gestation is 496.8 mm, and is ´approximately 2.47 times longer than 201.5 mm from the fourth month.
9) Of the obliquity of *the umbilical cord, the highest frequency is found at the counter-clock-wise distorsion.
10) From the quantitative tissue analysis, about 17 to 20 per cent of the tissue is occupied by the intervillous space.
11) From the above analysis, about 15.5 per cent of the tissue is occupied by the syncitium bud from the placenta of the second month of gestation, and is decreased with the time until the tenth month at which only 2.0 per cent of the tissue is the syncitium bud. The mean value of the diameter of the bud is 69.8 micra at the sencond month, is gradually decreased with the time, and is reached at 28.1 micra from those of the tenth month delivery.
12) The cytotrophoblastic cell column is able to be observed by the fourth month, and has the diameter of about two hundred micra.
13) The diameter of. the placental villi is ranged between 30 to 150 micra. The villi are bigger with scanty in number during the early half of the gestation, but those situation is reversed during the later half of the gestation.
14) The villus stems are classified in accordance with the diameters of the stems, such as, the
primary atem(1500-500 micra), secondary stem(500-300 micra), and the tertiary stem (300-150 micra). The villus stems are rich in number during the early half of the gestation, and are decreased with the time.
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