The primitive gut forms during the 4th week of the development as a result of cephalocaudal and lateral folding of the embryo. This endoderm lined cavity is incorporated into the embryo, while the yolk sac and the allantois remain temporarily by outside the embryo.
The endoderm of the primitive gut gives rise to the epithelium and glands of the digestive tract. The muscular and fibrous elements of the digestive tract are derived from the splanchnic mesoderm. The epithelium at the cranial and caudal extremities of the digestive tract is derived from the ectoderm of the stomodeum and the proctodeum (anal pit).

1. Foregut
2. Hindgut
3. Midgut
4. Central nervous system
5. Tracheobronchial diverticulum
6. Heart
7. Liver bud
8. Buccopharyngeal membrane
9. Vitelline duct
10. Allantois
11. Cloacal membrane

1. Yolk sac
2. Surface ectoderm
3. Amniotic cavity
4. Neural groove
5. Splanchnic mesoderm
6. Somatic mesoderm

1. Yolk sac
2. Surface ectoderm
3. Amniotic cavity
4. Neural tube
5. Splanchnic mesoderm
6. Somatic mesoderm

1. Gut endoderm
2. Intraembryonic coelomic cavity
3. Amniotic cavity
4. Dorsal mesentery
5. Splanchnic mesoderm
6. Somatic mesoderm
7. Neural tube

The primitive gut is divided into four parts: a) the pharyngeal gut which extends from the buccopharyngeal (oropharyngeal) membrane to the respiratory (tracheobronchial) diverticulum; b) the foregut, extending from the tracheobronchial diverticulum to the liver outgrowth; c) the midgut, extending from the liver outgrowth to the junction of the right two thirds and left one third of the transverse colon in the adult (posterior intestinal porta); and d) the hindgut, extending from the posterior intestinal porta to the cloacal membrane.
The liver, biliary apparatus, pancreas and the respiratory system arise as diverticula from the foregut.
Along the entire length, the intestinal tube is suspended from the dorsal body wall by a dorsal mesentery. Along the segment of its length, it is attached to the ventral body wall by a ventral mesentery.

1. Foregut
2. Stomach
3. Hindgut
4. Midgut
5. Pharyngeal gut
6. Esophagus
7. Tracheobronchial diverticulum
8. Buccopharyngeal membrane
9. Cloacal membrane
10. Stomodeum
11. Cloaca
12. Gallbladder
13. Liver
14. Pancreas
15. Vitelline duct
16. Allantois