A unilateral cleft lip is formed when:

A unilateral cleft lip is formed when:

1. a-  The palatal shelves remain in a vertical position.

2. b-  The bucco-nasal membrane ruptures.

3. c-  One maxillary process fails to fuse with the medial nasal process.

4. d-  One lateral nasal process fails to fuse with the maxillary process.