Final answer:
To achieve a proper lateral projection of the humerus, the humeral epicondyles should be positioned perpendicular to the Image Receptor (IR).
Step-by-step explanation:
The question asks what the relationship is between the humeral epicondyles and the Image Receptor (IR) to achieve a proper lateral projection of the humerus. For a proper lateral projection of the humerus during an X-ray, the humeral epicondyles should be positioned perpendicular to the IR. This orientation ensures that the lateral aspect of the humerus is accurately imaged, providing a clear view of the lateral humeral structure for diagnostic purposes.