Figure 44.14 illustrates muscle attachments in arthropod exoskeletons. Endoskeletons Vertebrates have endoskeletons of cartilage, bone, or a combination of both. Cartilage is more flexible than bone. Osteoblasts lay down new bone matrix and become surrounded by the matrix. Once surrounded, osteoblasts become the maintenance cells called osteocytes .
Osteoclasts break down bone matrix and help recycle calcium and repair and reshape bone.
Figure 44.15 illustrates the human skeleton. Figure 44.17 illustrates endochondral bone formation in a long bone. In conjunction with muscles, bones work as levers to bring about movement. Tendons join muscle to bone or muscle to muscle. Ligaments join bone to bone.