Which of the following is classified as a long bone?

A long bone is primarily characterized by its elongated shaft (diaphysis) and distinct ends (epiphyses). Long bones are typically found in the limbs and are crucial for various movements as they serve as levers. The distal phalanx of the second toe is indeed classified as a long bone because it possesses the typical structure of a long bone despite its smaller size. It has a shaft and two ends, fulfilling the criteria of long bone classification.

The scapula, while an essential component of the shoulder girdle, is considered a flat bone due to its thin, flattened shape, which aids in protecting underlying structures. The patella is classified as a sesamoid bone, which means it is embedded within a tendon. Lastly, carpals are categorized as short bones because they are roughly cube-shaped and designed for stability rather than movement. Thus, the distal phalanx is the correct choice when identifying a long bone among the options provided.