The endoderm is the innermost of the three embryonic germ layers.  It lies beneath the ectoderm and mesoderm.  This germ layer gives rise to:

- the epithelial lining of the respiratory tract
- the gastrointestinal tract
- accessory organs of the digestive tract

Michigan State University

The germ layers are the three layers of the embryo that are formed in the gastrulation process.  They give rise to all of the tissues of the body except for germ cells.  The layers include:

- endoderm
- mesoderm
- ectoderm

Germ Layers

Barresi, M. J., &amp; Gilbert, S. F. (2020). Developmental Biology (12th ed.). New York: Sinauer.

Developmental Biology (12th ed.)

Endoderm

The mesoderm is the middle of the three embryonic germ layers.  It lies in between the endoderm and the ectoderm.  This germ layer gives rise to:

- muscles
- skeleton
- connective tissue
- the urogenital system
- blood
- blood vessels
- part of the heart

Mesoderm

The ectoderm is either the outside (in amphibians) or dorsal (in birds and mammals) surface of the embryo after gastrulation.  This germ layer gives rise to:

- neural tube
- neural crest
- epidermis

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