In amniote

Amniote

The amniotes are a group of tetrapods that have a terrestrially adapted egg. They include synapsids and sauropsids , as well as their fossil ancestors. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes...

 animal embryology

Embryology

Embryology is a science which is about the development of an embryo from the fertilization of the ovum to the fetus stage...

, the epiblast is a tissue type derived either from the inner cell mass

Inner cell mass

In early embryogenesis of most eutherian mammals, the inner cell mass is the mass of cells inside the primordial embryo that will eventually give rise to the definitive structures of the fetus...

 in mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s or the blastodisc in birds and reptiles. It lies above the hypoblast

Hypoblast

The hypoblast is a tissue type that forms from the inner cell mass. It lies beneath the epiblast and consists of small cuboidal cells.Extraembryonic endoderm is derived from hypoblast.-External links:...

.

Mammals

In mammalian embryogenesis

Mammalian embryogenesis

Mammalian embryogenesis is the process of cell division and cellular differentiation during early prenatal development which leads to the development of a mammalian embryo.-Difference from human embryogenesis:...

, the columnar cells of the epiblast are adjacent to the trophoblast

Trophoblast

Trophoblasts are cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta. They are formed during the first stage of pregnancy and are the first cells to differentiate from the fertilized egg...

, while the cuboidal cells of the hypoblast

Hypoblast

The hypoblast is a tissue type that forms from the inner cell mass. It lies beneath the epiblast and consists of small cuboidal cells.Extraembryonic endoderm is derived from hypoblast.-External links:...

 are closer to the blastocoele

Blastocoele

A blastocoel or blastocele is the fluid-filled central region of a blastocyst...

. The epiblast, whilst referred to as the primary ectoderm, differentiates to form all three layers of the trilaminar germ disc in a process called gastrulation

Gastrulation

Gastrulation is a phase early in the embryonic development of most animals, during which the single-layered blastula is reorganized into a trilaminar structure known as the gastrula. These three germ layers are known as the ectoderm, mesoderm, and endoderm.Gastrulation takes place after cleavage...

.

Epiblast diversity

Human epiblast is disc-shaped as opposed to the mouse epiblast which is cup-shaped.

External links

• http://www.embryology.ch/allemand/iperiodembry/carnegie02.html
• http://www.med.umich.edu/lrc/coursepages/M1/embryology/embryo/04secondweek.htm
• http://isc.temple.edu/marino/embryology/EMBII97/sld005.htm