What is the term for bones that are not classified into any specific group?

The correct term for bones that do not fit into any specific group is irregular bones. Irregular bones are characterized by their complex shapes and are not categorized as long, short, flat, or sesamoid bones. These bones include the vertebrae, sacrum, and certain bones of the face. Their irregular shapes are often adapted to their specific functions within the body.

Sesamoid bones, while an important category, are specifically defined as small bones that develop within tendons, most notably the patella. Flat bones, such as the skull and ribs, have a specific flattened shape. Cuboidal bones, while not a formally recognized category in human anatomy, could refer to short bones that resemble cubes, like those in the wrist and ankle. Thus, the unique characteristics of irregular bones distinguish them as a group that does not conform to the other classifications.