Which rib is known for not having a direct attachment to the sternum?

Rib 9 is identified as a false rib, meaning it does not have a direct attachment to the sternum. Instead, it is connected to the costal cartilage of the rib above it (rib 8). This characteristic distinguishes false ribs from true ribs, which attach directly to the sternum through their own costal cartilage. True ribs include ribs 1 to 7, which connect directly and securely to the sternum.

Rib 1, the first rib, is commonly associated with unique anatomical features such as being flat and broad, as well as having a direct connection to the sternum. Rib 7 is also part of the true ribs and has a direct attachment to the sternum. Rib 5, although it does not specifically have a unique characteristic that distinguishes it in this context, is also a true rib with direct attachment. Therefore, these options do not fit the criteria for the correct answer, which focuses on the rib's lack of direct attachment to the sternum.