Editing Germ layer (section)

===Endoderm===
[[Image:Endoderm2.png|thumb|200px|The [[endoderm]] produces tissue within the [[lung]]s, [[thyroid]], and [[pancreas]].]]
{{main|Endoderm}}

The '''endoderm''' is one of the germ layers formed during animal [[embryonic development]]. Cells migrating inward along the [[archenteron]] form the inner layer of the [[gastrula]], which develops into the [[endoderm]].

The endoderm consists at first of flattened cells, which subsequently become columnar. It forms the epithelial lining of the whole of the [[gastrointestinal tract|digestive tract]] except part of the mouth and pharynx and the terminal part of the rectum (which are lined by involutions of the ectoderm). It also forms the lining cells of all the glands which open into the digestive tract, including those of the liver and pancreas; the epithelium of the auditory tube and tympanic cavity; the trachea, bronchi, and alveoli of the lungs; the bladder and part of the urethra; and the follicle lining of the thyroid gland and thymus.

The endoderm forms: the [[pharynx]], the [[esophagus]], the [[stomach]], the [[small intestine]], the [[large intestine|colon]], the [[liver]], the [[pancreas]], the [[urinary bladder|bladder]], the [[epithelial]] parts of the [[trachea]] and [[bronchi]], the [[lungs]], the [[thyroid]], and the [[parathyroid]].