You assist to deliver a full term baby boy who is otherwise normal but has a left cleft of the upper lip that extends upward toward the left nostril and left anterior cleft of the primary palate just deep to the cleft lip. These defects are most likely due to a failure of which of the following?

The lateral nasal process forms the alar region of the nose. Normally the maxillary process moves medially and fuses with the medial nasal process at the philtrum on both sides of the upper lip. The fact that the cleft involves both the lip and bony primary palate suggests failure of the maxillary process to fuse with the medial nasal process. The mandibular process does not normally fuse with either the lateral or medial nasal processes. That would reduce the size of the mouth. The lateral and medial nasal processes fuse to form a nostril separate from the oral cavity