A bony endoskeleton serves several purposes. Because bones are hard and dense, they give the body both structure and strength. Some bones, like those that make up the skull and rib cage, provide protection for vital organs. And some bones work like factories, creating red blood cells inside the spongy marrow tissue found within their hard, dense exterior.
Many bones, like those in the legs and arms, are involved in movement. As muscles flex, they pull bones into different positions, moving limbs and other body parts. Bones connect at joints, which bend, allowing the bodies of organisms with bony endoskeletons to be flexible.
Different vertebrate species have varied numbers and arrangements of bones in their endoskeletons. While a giraffe’s neck can stretch to about 2 meters (6 feet) long, it is made up of only seven vertebra bones—the same number as in humans. And who is the winner for most bones in the animal kingdom? That award goes to enormous snakes called pythons, which can measure more than 9 m (30 ft) long, thanks to their approximately 1,800 bones.