What does "flat sided" refer to in a dog's anatomy?

"Flat sided" in a dog's anatomy specifically refers to the ribs being insufficiently rounded near the sternum. This term is often used in the context of evaluating a dog's physical structure, particularly in breeds that are expected to have a more rounded ribcage for efficient lung capacity and overall health. A flat-sided appearance can be an indication of a poor physique in certain breeds, affecting their performance and stamina.

In contrast, the other options do not accurately relate to what "flat sided" describes. A condition of underweight speaks more to overall body condition rather than specific anatomical structure. The shape of the skull pertains to the cranium and is independent of rib structure. Ear posture describes how a dog's ears are held and does not connect to the ribcage or general body shape. Hence, recognizing “flat sided” as it relates to the ribs is crucial for assessing a dog’s conformation and potential health issues.