Which facial prominence forms the upper lip and primary palate?

The facial prominence that forms the upper lip and primary palate is the medial nasal prominence. Here are the steps of how it forms:

1. During the embryonic development, five facial prominences appear around the stomodeum (primitive mouth) - one frontonasal prominence, two maxillary prominences, and two mandibular prominences.

2. The frontonasal prominence is divided into two medial nasal prominences and two lateral nasal prominences by the nasal pits (which later form the nostrils).

3. The medial nasal prominences merge in the midline to form the intermaxillary segment.

4. This intermaxillary segment gives rise to the philtrum of the upper lip, the primary palate (the anterior part of the hard palate), and the upper jaw central incisor teeth.

5. The maxillary prominences grow medially and merge with the medial nasal prominences. This forms the rest of the upper lip.

6. The primary palate then fuses with the secondary palate (formed from the maxillary prominences) to form the complete hard palate.

So, in summary, the upper lip and primary palate are formed from the medial nasal prominences.