femur, upper bone of the leg or hind leg. The head forms a ball-and-socket joint with the hip (at the acetabulum), being held in place by a ligament (ligamentum teres femoris) within the socket and by strong surrounding ligaments. In humans the neck of the femur connects the shaft and head at a 125° angle, which is efficient for walking. A prominence of the femur at the outside top of the thigh provides attachment for the gluteus medius and minimus muscles. The shaft is somewhat convex forward and strengthened behind by a pillar of bone called the linea aspera. Two large prominences, or condyles, on either side of the lower end of the femur form the upper half of the kneejoint, which is completed below by the tibia (shin) and patella (kneecap). Internally, the femur shows the development of arcs of bone called trabeculae that are efficiently arranged to transmit pressure and resist stress. Human femurs have been shown to be capable of resisting compression forces of 800–1,100 kg (1,800–2,500 pounds).
The femur in humans is long and relatively slender or delicate; in the great apes it is shorter, more curved, and more robust. The orangutan lacks a ligamentum teres femoris, allowing for nearly complete rotary action of the lower limb but decreasing strength and stability.
Keep Learning
How do bones grow and repair themselves?
What makes the human skeleton different from other animals?
Why are joints important and how do they work?
How do muscles attach to bones to create movement?
What are the most common types of bone fractures and how do they heal?
What are the two main subdivisions of the human skeleton?
The human skeleton has two main subdivisions: the axial skeleton, which includes the vertebral column and much of the skull, and the appendicular skeleton, which includes the pelvic and pectoral girdles and the bones and cartilages of the limbs.
What are the primary functions of the human skeleton?
The primary functions of the human skeleton are support, protection, and motion. Support is the most primitive and oldest function, while protection involves safeguarding organs, and motion is enabled by the skeletal muscles anchored to bones.
How does the human skeleton protect the central nervous system?
The central nervous system is protected by the axial skeleton, with the brain enclosed in the cranium and the spinal cord protected by the vertebral column and bony neural arches.
What is the role of the hyoid bone?
The hyoid bone serves as an anchoring structure for the tongue. It is situated at the root of the tongue in the front of the neck and does not articulate with other bones.
What is unique about the structure of the human vertebral column?
The human vertebral column is S-shaped, which helps with absorbing shock, distributing weight, and maintaining balance while upright. This curvature provides flexibility, enabling a great range of motion, while also supporting the trunk and providing space for the viscera.
human skeleton, the internal skeleton that serves as a framework for the body. This framework consists of many individual bones and cartilages. There also are bands of fibrous connective tissue—the ligaments and the tendons—in intimate relationship with the parts of the skeleton. This article is concerned primarily with the gross structure and the function of the skeleton of the normal human adult.
The human skeleton, like that of other vertebrates, consists of two principal subdivisions, each with origins distinct from the others and each presenting certain individual features. These are (1) the axial, comprising the vertebral column—the spine—and much of the skull, and (2) the appendicular, to which the pelvic (hip) and pectoral (shoulder) girdles and the bones and cartilages of the limbs belong. A third subdivision, the visceral (splanchnocranium), comprises the lower jaw, some elements of the upper jaw, and the branchial arches, including the hyoid bone.
When one considers the relation of these subdivisions of the skeleton to the soft parts of the human body—such as the nervous system, the digestive system, the respiratory system, the cardiovascular system, and the voluntary muscles of the muscle system—it is clear that the functions of the skeleton are of three different types: support, protection, and motion. Of these functions, support is the most primitive and the oldest; likewise, the axial part of the skeleton was the first to evolve. The vertebral column, corresponding to the notochord in lower organisms, is the main support of the trunk.
The central nervous system lies largely within the axial skeleton, the brain being well protected by the cranium and the spinal cord by the vertebral column, by means of the bony neural arches (the arches of bone that encircle the spinal cord) and the intervening ligaments.
A distinctive characteristic of humans as compared with other mammals is erect posture. The human body is to some extent like a walking tower that moves on pillars, represented by the legs. Tremendous advantages have been gained from this erect posture, the chief among which has been the freeing of the arms for a great variety of uses. Nevertheless, erect posture has created a number of mechanical problems—in particular, weight bearing. These problems have had to be met by adaptations of the skeletal system.
Human skeletonA diagram of the human skeleton showing bone and cartilage.
Protection of the heart, lungs, and other organs and structures in the chest creates a problem somewhat different from that of the central nervous system. These organs, the function of which involves motion, expansion, and contraction, must have a flexible and elastic protective covering. Such a covering is provided by the bony thoracic basket, or rib cage, which forms the skeleton of the wall of the chest, or thorax. The connection of the ribs to the breastbone—the sternum—is in all cases a secondary one, brought about by the relatively pliable rib (costal) cartilages. The small joints between the ribs and the vertebrae permit a gliding motion of the ribs on the vertebrae during breathing and other activities. The motion is limited by the ligamentous attachments between ribs and vertebrae.
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The third general function of the skeleton is that of motion. The great majority of the skeletal muscles are firmly anchored to the skeleton, usually to at least two bones and in some cases to many bones. Thus, the motions of the body and its parts, all the way from the lunge of the football player to the delicate manipulations of a handicraft artist or of the use of complicated instruments by a scientist, are made possible by separate and individual engineering arrangements between muscle and bone.
In this article the parts of the skeleton are described in terms of their sharing in these functions. The disorders and injuries that can affect the human skeleton are described in the article bone disease.
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