A quick start to the skeleton

4 minute read

In this course, you will be working extensively with skeletal anatomy. The skeleton provides the primary evidence about our evolutionary history. Skeletal evidence is a limited source of information about biology, but soft tissue evidence is fragile and does not persist long even in curated museum contexts. So a disproportionate fraction of our knowledge about anatomical variation comes from the skeleton.

Fortunately anthropologists have been very clever in finding evidence that connects skeletal anatomy to behavior and other aspects of biology. Nowadays bone and teeth provide some of the strongest evidence about diet, development and health of ancient human and primate populations. We are even getting new genetic evidence from bone and teeth, including the complete genomes of archaic humans.

Knowing the skeleton is an essential skill in biological anthropology. Most students will enter this class with a basic knowledge of the bones of the skeleton, and this lab station should help remind you about the parts you probably already know.

Basic divisions of the skeleton

The skull, or cranium sits atop the spine. The rest of the skeleton, everything from the neck down, is called the postcranium, or postcranial skeleton

The skull itself is a complicated structure made up of 26 cranial bones plus the mandible. Except for the mandible, these bones mostly are fused together so that they do not move. The joints between most of the cranial bones are borders where the bones knit together, called sutures. You will learn most of the major bones of the cranium in this class. For now, be sure to remember the mandible.

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.

The postcranial skeleton can be roughly divided into the appendicular skeleton, which includes the arms, legs, hands and feet, and the axial skeleton, which includes everything else.

The long bones

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

The axial skeleton

The spinal column makes up the connection between upper and lower parts of the skeleton. It is made up of 24 vertebrae in most people. Twelve of the vertebrae connect to twelve pairs of ribs. These numbers vary within humans, and between humans and other kinds of primates, and that variation will be the subject of a lab.

Each shoulder girdle is composed of the scapula, or shoulder blade, and that clavicle, or collar bone. At the front of the chest is a flat bone called the sternum that connects ribs by means of the costal cartilages.

Finally, at the lower end of the axial skeleton is the pelvis. This structure is composed of three bones, the sacrum at the base of the spine, and the left and right os coxae or innominate bones. The pelvis is also the subject of an entire lab in this course.

Practice

That quick introduction will help to orient you toward the skeleton. Remember that each of the bones can be found within your own body, and for the most part you can feel them from the outside. In total, the human skeleton has more than 206 bones – more because there are minor bones within tendons that vary in number in different people. Humans are variable, as you will discover during the course of this semester, and not everyone has the same numbers of bones or the exact same arrangement.