What distinguishes the radius from the ulna?

The radius is distinguished from the ulna primarily by its position relative to the elbow. In an anatomical position, the radius is located on the lateral side of the forelimb (or the thumb side in humans) when the body is facing forward, while the ulna is situated medially (or on the pinky side). This orientation is significant because it allows for the rotation of the forearm; the radius can pivot around the ulna during movements such as pronation and supination.

Understanding the spatial relationship between the radius and ulna is fundamental in veterinary medicine, especially when examining forelimb injuries or conditions affecting these bones. The other choices, while related to anatomical considerations, do not specifically highlight the distinguishing feature relevant to the question. For example, the location in the hind limb pertains to different bones altogether, while size in relation to the tibia involves a different set of bones entirely. Lastly, the type of connective tissue doesn't differentiate these two bones since both are classified under similar connective tissues in anatomical terms.