The humerus and also the femur are matching bones that the arms and also legs, respectively. When their components are comparable in general, your structure has actually been adapted to different functions. The head the the humerus is practically hemispherical, while the of the femur forms about two-thirds that a sphere. There is a strong ligament passing native the head of the femur to more strengthen and also ensure its position in the acetabulum.
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The anatomical neck the the humerus is only a slim constriction, while the neck of the femur is a an extremely distinct portion, to run from the head to accomplish the tower at an edge of about 125°. Actually, the femoral neck is developmentally and also functionally a part of the shaft. The whole weight the the human body is directed with the femoral heads along their necks and to the shaft. The framework of the bone within the head and neck and also the upper part of the tower of the femur would execute credit to an engineer who had cleared up the weight-bearing problems associated in the maintain of upright posture.
(Left) The radius and the ulna, skeleton of the forearm; (right) the fibula and the tibia, bones of the lower leg.
At the elbow, the ulna forms with the humerus a true hinge joint, in i m sorry the actions room flexion and extension. In this share a big projection that the ulna, the olecranon, fits right into the well-defined olecranon fossa, a depression of the humerus.
The radius is shorter than the ulna. Its most distinctive function is the special disk-shaped head, which has a smoothly concave premium surface come articulate with the head, or capitulum, of the humerus. The head the the radius is held against the notch in the next of the ulna by method of a solid annular, or ring-shaped, ligament. Although therefore attached come the ulna, the head the the radius is complimentary to rotate. Together the head rotates, the shaft and also outer finish of the radius room swung in one arc. In the position of the arm referred to as supination, the radius and also ulna space parallel, the palm the the hand faces forward, and also the ignorance is away from the body. In the position referred to as pronation, the radius and also ulna room crossed, the palm encounters to the rear, and also the ignorance is next to the body. There space no action of the leg equivalent to the supination and also pronation of the arm.
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The radius and ulna (bones of the forearm), displayed in supination (the arm rotated outward so that the palm that the hand encounters forward).