A craniate or vertebrate is that the unborn offspring of associate associateimal that develops from an embryo. Following embryonic development the vertebrate stage of development takes place. In human prenatal development, vertebrate development begins from the ninth week when fertilisation and continues till birth.
Biologists every which way speak of the earliest stages of development of the beast as the embryonic period, that ends once the external style of the embryo begins to fit clearly the newborn of the cluster to that it belongs. succeeding amount, culminating in birth, is the fetal amount. In human development this transition happens in more or less the eighth week after conception. The vertebrate stage is characterised by enhanced growth and by the complete development of the organ systems.
Amniotic sac. A thin-walled sac that surrounds the craniate throughout maternity. The sac is crammed with liquid created by the craniate (amniotic fluid) and the membrane that covers the vertebrate aspect of the placenta (amnion). This protects the craniate from injury. it conjointly helps to manage the temperature of the craniate.