What is the composition of vertebrae?

The correct answer is based on the structure and composition of vertebrae, which are primarily made up of both bony and cartilaginous elements. Vertebrae consist of a central body that is composed of cancellous bone, surrounded by a hard outer layer of compact bone. They are connected by intervertebral discs, which are comprised of fibrocartilage, allowing for both support and flexibility in the spinal column. This unique combination of bone and cartilage is essential for providing the necessary range of motion, cushioning, and protection of the spinal cord.

The other options do not accurately reflect the anatomy of vertebrae. Hollow bones generally refer to larger bones that contain a medullary cavity, which is not representative of vertebrae due to their complex and denser structure. Long bones, such as femurs and humeri, are characterized by a greater length than width and have a shaft with ends, which does not match the form of vertebrae. Flat bones, like the sternum or cranial bones, serve different functions and shapes, making them distinct from the irregularly shaped vertebrae. Therefore, the classification as cartilaginous bones acknowledges the significant role of cartilage in their structure and function within the spine.