Which bone runs two-thirds the length of the ear canal?

The temporal bone is the correct answer because it plays a crucial role in the anatomy of the ear. The external auditory canal, also known as the ear canal, is partly formed by the temporal bone, which houses important structures of the ear, including the middle and inner ear components.

The ear canal itself is approximately 2.5 cm in length, and the temporal bone contributes a significant portion of this canal. Its presence is vital for protecting the inner structures of the ear and facilitating sound transmission. Moreover, the temporal bone has features such as the mastoid process and the squamous part which are integral to the overall architecture of the ear, relating to hearing and balance functions.

Other bones listed in the options, like the maxilla, frontal bone, and zygomatic bone, do not have a direct anatomical connection with the ear canal, making them irrelevant in this context. The maxilla is a facial bone primarily involved in the structure of the face and upper jaw, while the frontal bone forms the forehead and contributes to the orbits of the eyes. The zygomatic bone, also known as the cheekbone, is important for facial structure but not related to the ear canal's anatomy. This is why the temporal bone is the most appropriate answer