Which plane connects the gonion to the gnathion and the gonion to the menton?

The correct answer is the mandibular plane, as it is specifically defined by the connection of the gonion (the midpoint of the contour of the ramus) to the gnathion (the most inferior point on the symphysis of the mandible) and from the gonion to the menton (the lowest point on the mandible). This anatomical configuration allows the mandibular plane to serve as a reference for various morphometric measurements in cephalometric analysis, and it is critical for understanding the positioning of the mandible in relation to the rest of the skull.

The other options, while relevant in cephalometric assessment, do not specifically describe the connections outlined in the question. The SN plane (sella-nasion plane) primarily references the relationship between the sella turcica and the nasion, which pertain to cranial measurements rather than mandibular structure. The palatal plane is defined by the maxillary occlusal surface and is important in dental assessments, but does not connect the structures mentioned. The facial plane relates to the orientation of the face in a broader sense, encompassing points such as the nasion and the gonion but not specifically measuring the outlined mandibular components.