Final answer:
The facial bones seen in the lower third of the orbits include the maxillae and the zygomas. The orbital rim mentioned refers to part of the frontal bone, while the nasal septum and anterior nasal spine don't directly contribute to the orbits' structure.
Step-by-step explanation:
Facial Bones Visible in the Lower Third of the Orbits and the Petrous Ridges
The lower third of the orbits and the petrous ridges involve several facial bones. The orbital rim is part of the frontal bone and contributes to the superior margin of the orbit. The maxillae form a significant portion of the facial skeleton, comprising the upper jaw and the floor of the orbit. The nasal septum consists of both bone and cartilage; however, it does not directly contribute to the structure of the orbits. The zygomas, or cheekbones, are part of the lateral and inferior borders of the orbits. Lastly, the anterior nasal spine is a bony projection of the maxilla, supporting the cartilage of the nose but doesn't contribute to the lower third of the orbits.
Among these structures, the ones mainly relevant to the lower third of the orbits and the petrous ridges are the maxillae and zygomas. The petrous ridges, which are part of the temporal bone, are not facial bones and thus are not among the options provided.