The central area of the two limbs of a horseshoe-shaped mesenchymal swelling that lie medial to the olfactory placode or pit in the future nasal region of the embryo; it joins with the ipsilateral maxillary prominence in the formation of half of the upper jaw, and the nasal tip and philtrum of the upper lip develop from it.
Comment:
[development-note] "Fusion of right and left medial nasal processes forms a primary palate rostrally and the nasal septum caudally. The incisive bone, including upper incisor teeth and the rostral up- per lip, are derived from the primary palate. The nasal septum consists of bone, cartilage, and a patch of soft tissue membrane that separates right & left halves of the nasal cavity."