Learning about the skeleton has many applications in biological anthropology. Forensic scientists and bioarchaeologists rely upon a knowledge of the skeleton to understand the lives of deceased people and populations. Specialists in primate biology and evolution connect differences in the shapes and sizes of bones to the lifestyles and environments of different species. Paleoanthropologists understand the process of human origins by examining evidence from bones.

A human skeleton has more than 200 bones. Many textbooks say 206, but actually the precise number varies among different people. The canonical number of 206 bones includes the ones that have well-defined names and occur in nearly all people. Most adults have additional bones that are not counted in this number, such as the sesamoid bones of the feet and (sometimes) hands.

Anatomists have a name for every bone of the skeleton and names for the main features found on each bone. Learning all these names can be a long process. One way to start is by understanding the main anatomical regions of the skeleton.

Basic divisions of the skeleton

• The cranium, or skull, sits atop the spine. The rest of the skeleton, everything from the neck down, is called the postcranium, or postcranial skeleton.
• Human anatomists sometimes use the term infracranial (infra- = "beneath") rather than postcranial (post- = "behind").
• A different way of dividing the skeleton is into the appendicular skeleton, which includes the arms, legs, hands, feet, shoulder girdle, and hip bones, and the axial skeleton, which includes the skull, vertebral column, ribs, sternum, and sacrum. This division reflects the central axis of the skeleton versus the legs and arms and parts that connect them.

Cranium

The skull itself is a complicated structure made up of 27 cranial bones plus the mandible. Except for the mandible, these bones mostly are fused together so that they do not move relative to each other.

The joints between most of the cranial bones are borders where the bones knit together, called sutures.

The teeth are rooted in the mandible and the bones of the face, called the maxillary bones, or maxillae. The teeth are the only part of the skeletal system that come into direct contact with the environment. They are not bone, but are instead made up of hard calcified tissues called dentin and enamel. The teeth are small but contain a vastly outsized fraction of information because of their long persistence in the fossil record as well as their close relationship to development and diet.

You will learn most of the major bones of the cranium in this series of virtual labs. For now, be sure to remember the mandible.

Appendicular skeleton

The long bones are the major bones of the arm and leg. These bones are variations on a common theme: A long shaft with two ends, each of which forms part of an articulation, or joint, with another bone or structure.

The long bones are all paired bones, meaning that each individual has both a left and right. The anatomy of the each bone enables us to identify whether it came from the right or left side of the skeleton.

The bones of the leg include the femur, tibia and fibula. The femur is the thigh bone, the tibia is the shin bone, and the fibula is a thin bone at the outside of the leg, mainly noticeable because it forms the outside of the ankle joint.

The bones of the arm are the humerus, ulna and radius. The humerus is in the upper arm, the radius and ulna are the lower arm bones. These two bones rotate around each other, and are mostly obvious at the wrist and elbow joint. The ulna is the bone that is most prominent on the back of the elbow. The radius is the lower arm bone that lies nearer the thumb, the ulna is nearer the pinky side of the hand.

Each shoulder girdle is composed of the scapula, or shoulder blade, and the clavicle, or collar bone.

The pelvis is a structure that includes the left and right os coxae or innominate bones, and the sacrum, which is part of the axial skeleton.

Axial skeleton

• The cranium, discussed above, is the superior end of the axial skeleton.
• The vertebral column runs the length of the back. Most people have 24 vertebrae.
• Usually, twelve of the vertebrae connect directly to twelve pairs of ribs. In some people this number may be thirteen or eleven, or the number may be different on left and right sides.
• At the front of the chest is a flat bone called the sternum that connects ribs by means of the costal cartilages.
• The sacrum is composed of fused vertebrae at the base of the vertebral column. This structure is part of the pelvis and connects the left and right hip bones, or ossa coxae. At the most inferior end of the sacrum, a few small vertebral bodies form the coxxyx, or tailbone.

Materials in this lab

• The human skeletal 3D models in this virtual lab have been provided under a Creative Commons license by The Database Center for Life Science, Japan. The license is CC Attribution-Share Alike 2.1 (CC-BY-SA). These are anatomical models created by digital artists based on their study of human anatomy. For this virtual lab, all models have been reduced substantially in polygon count. The original, full-resolution models can be found on the BodyParts3D website.

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