Articles written in Proceedings – Animal Sciences
Volume 87 Issue 6 June 1978 pp 91-104
The embryo of
Volume 87 Issue 9 September 1978 pp 179-194
The amnion expands to accommodate the growing foetus without undergoing any noticeable histological change. The yolk sac is large and forms an extensive chorio-vitelline placenta on the lateral sides of the uterus during early stages of gestation. However, due to the extension of the exocoelom and the expansion of the amniotic cavity the vascular splanchnopleure of the yolk sac is separated from the placenta and is invaginated towards the abembryonic trilaminar omphalopleure. The endodermal cells of the yolk sac hypertrophy as the yolk-sac wall gets vascularized, and the mesodermal cells enlarge only during the final stages of pregnancy. The allantoic vesicle, which is large during early stages of gestation, becomes progressively reduced and is finally lost during the final stages of pregnancy. The placenta, which is extensive during early stages, becomes restricted to a discoidal structure on the mesometrial side of the uterus. The definitive placenta is labyrinthine and vasomonochorial. Numerous free chorionic villi, which come into direct contact with the decidua at the margin of the placental disc, constitutes an accessory syndesmochorial placenta.
Volume 93 Issue 5 September 1984 pp 463-483
The development of foetal membranes and the changes in the structure of the placenta in the bat
Volume 98 Issue 3 May 1989 pp 149-166
Volume 99 Issue 4 July 1990 pp 289-303
Vascularisation of the placenta of several species of bats representing 8 families is reported. Maternal vascularisation in all these bats is effected by a few large vessels which pass through the entire thickness of the placenta and give rise to numerous radial branches on reaching the foetal surface of the placenta. Maternal blood is returned through placental tubules which empty into large venous channels at the utero-placental junction. Foetal vascularisation is brought about by two allantoic arteries which capillarise over the placental tubules, and a large allantoic vein. In the exchange areas there is mostly crosscurrent circulation of the maternal and foetal bloods. Only in emballonurid bats is there an haematoma from which maternal blood is not drained back but is absorbed by cells of the trophoblast of chorionic villi.