Question

With respect to rib cage, explain the following:
A. Bicephalic ribs
B. True ribs
C. Floating ribs

Answer 1

The rib cage encloses and protects vital organs like the heart, lungs etc in most vertebrates. It is made up of ribs connected to the vertebral column and sternum in the thorax. The thoracic cage, which is made up of the rib cage and the sternum, is a semi-rigid bony and cartilaginous structure that covers the thoracic cavity and supports the shoulder girdle to form the central portion of the human skeleton. The protective cage of the thorax is formed by the ribs, which are made up of $24$ bones in $12$ pairs. True ribs and false ribs refer to rib pairs that are connected to the sternum directly or indirectly.

Complete explanation:
A. Bicephalic ribs: The ribs are divided into $12$ pairs. Each rib is a thin flat bone that connects the vertebral column dorsally and the sternum ventrally. It is called bicephalic since it has $2$ articulation surfaces on its dorsal end.
B. True ribs: The first $7$ pairs of ribs are known as true ribs. These ribs are fused to the thoracic vertebrae on the dorsal side and bound to the sternum on the ventral side by hyaline cartilage. The sternocostal joints attach the true ribs to the sternum.
C. Floating ribs: The last two pairs of ribs (${11^{th}}$ and ${12^{th}}$) are known as floating ribs because they are not attached ventrally to the sternum. Floating ribs are smaller and have cartilaginous tips. They are also known as the vertebral ribs because they are only attached to the thoracic vertebrae and have no attachment ventrally, thus the term "floating ribs."

Note:
Ribs are classified according to their position and relationship to the sternum. Both ribs are attached to the thoracic vertebrae posteriorly and are numbered one through $12$. True ribs are those that articulate directly with the sternum, while false ribs are those that do not. The true ribs are the first seven rib pairs, known as the fixed or vertebrosternal ribs, since they attach directly to the sternum; the false ribs are the next five pairs (${8^{th}}$ to ${12^{th}}$). Both vertebrochondral and vertebral ribs are included in the false ribs. The sternum is connected indirectly to the vertebrochondral ribs (${8^{th}}$ to ${10^{th}}$) through the costal cartilages of the ribs above them.