Costal Cartilage
Connective tissue (hyaline cartilage) associated with the axial skeleton
Also known as: Rib Cartilage
Classification
Connective tissue (hyaline cartilage) associated with the axial skeleton
Dimensions
These bars vary in length, with the segments near the middle of the chest being the longest and most curved, generally ranging from two to six inches depending on the specific rib they attach to.
Key Features
Look for smooth, slightly flattened segments that bridge the gap between the hard, hollow-centered rib bone and the flat breastbone in the center of the chest. In older specimens found in nature, these may become harder and resemble bone but often retain a more textured, pitted surface.
Similar Bones
These can be confused with the ribs themselves. You can tell them apart because the true rib is harder, more curved, and has a distinct head at the back end, while these segments are flatter and have blunt ends where they meet the breastbone.
Across Species
While humans have these flexible bars to allow the chest to expand, many other animals show fascinating variations. In birds, these segments have bony processes that overlap to strengthen the ribcage for flight. In turtles, similar structures are essentially absorbed into the developing shell to provide a rigid protective dome.
Evolutionary History
This tissue is a remnant of the early vertebrate skeleton, which was primarily made of cartilage before bone became the dominant structural material. It has been retained in the chest area of land-dwelling animals to provide a delicate balance between a rigid cage for protection and a flexible bellows for efficient breathing.
Photography Tips
Capture the point where this segment meets the breastbone. Use side-lighting to highlight the texture difference between the hard rib bone and this smoother connecting segment. Placing a ruler next to it helps show the varying widths of the different segments.
Notes
What is the highlighted blue part?