Final answer:
In periapical radiographs, the external oblique ridge is consistently seen above the internal oblique ridge, which is vital for understanding mandibular morphology and pathology.
Step-by-step explanation:
On periapical radiographs, the external oblique ridge is always seen above the internal oblique ridge. These anatomical features are important in the study of oral and maxillofacial regions and are consistently visible in this type of dental radiography. It is crucial to be able to distinguish these ridges as they can help in identifying the mandible's morphology and in the diagnosis of any dental or osseous pathology in the area.