In humans, it develops from the fourth pharyngeal pouch into the parafollicular cells of the thyroid to produce calcitonin.
In humans, the ultimopharyngeal body is an embryological structure, and is a derivative of the ventral recess of the fourth pharyngeal pouch.
[1][2] It is technically from the fifth pharyngeal pouch, but this is rudimentary and merges with the fourth.
[3] Endoderm cells migrate and associate with the ultimopharyngeal body during development.
In humans, the ultimopharyngeal body develops into the parafollicular cells of the thyroid.