In biology, the skeleton is a strong and often a rigid framework that supports the body of an animal, holding it upright and giving it shape and strength (Also skeletal system and, in special cases, shell or test).

The skeleton may be an exoskeleton (external, such as exists in many invertebrates) or an endoskeleton (internal, as in vertebrates. It may be mineralized, or not. It may be jointed, or not. If external, it may be moulted periodically, or not. This article is mostly about the human skeleton, an endoskeleton.

The average adult human skeleton has around 206 bones These bones meet at joints, the majority of which are freely movable, making the skeleton flexible and mobile. The skeleton also contains cartilage for elasticity. Ligaments are strong strips of fibrous connective tissue that hold bones together at joints, thereby stabilizing the skeleton during movement.

Skeletal Protection and Layout

A skeleton provides "cages" to protect the delicate organs. For example: the ribcage helps protect the lungs, heart, etc. Moreover, it gives muscles "sides" or edges to attach to (through tendons). It also maintains balance, supports the body's shape and allows for motion. Another function of the skeleton is to make red and white blood cells. The Marrow in the bone produces these cells for when the body needs them. But all these functions are perhaps secondary to the primary function of locomotion. The bones allow the muscles of the body to move the limbs. Bones come in different sizes; the longest bone is the femur, and the shortest, the stapes. The first layer of a bone is called the Periostium. It is a thin membrane coating the compact bone. The next layer of bones are called compact bones, and the middle, called spongy or cancellous bone, which are hollow and contain bone marrow. Joints of bones are held together by ligaments, which are fine fibers attaching to each bone at joints. In order for bones to not scrape against each other, slippery cartilage and synovial fluid are covered atop the bones.

The Skull

The human skull shapes the head and face, protects the fragile brain, and houses and protects special sense organs for taste, smell, hearing, vision, and balance. It is constructed from 22 bones, 21 of which are locked together by immovable joints, to form a structure of great strength.

The bony framework of the head is called the skull, and it is subdivided into 2 parts, namely;