What type of bones are sesamoid bones characterized as?

Sesamoid bones are generally characterized as flat and round in shape. These unique bones develop within tendons and are often found in locations where a tendon passes over a joint, such as the kneecap (patella). Their primary function is to protect the tendon, improve its mechanical advantage, and reduce friction.

This flat and rounded structure allows sesamoid bones to effectively bear weight and absorb pressure, enhancing the biomechanics of the joint they are associated with. For example, the shape of the patella helps in the smooth movement of the knee joint during activities like walking, running, and jumping.

The other options describe different types of bones. Long and narrow bones are typically found in the limbs, irregular and spongy bones have complex shapes (like vertebrae), while smooth and cylindrical bones do not specifically describe a recognized category of bone types within the skeletal system.