A human arm is composed of three bones, namely — humerus, ulna and radius. The arm of the human body is a crucial part that provides movement along the shoulder, elbow, wrist and fingers, which is useful for day to day activities. Below is a well-labelled diagram of arm bones for your better understanding.
Arm Bones – Diagram
- The humerus is the longest bone of the human arm that corresponds to the femur bone present in the legs.
- It extends from the shoulder till the elbow.
- It is composed of three main parts, the upper extremity, the body and the lower extremity.
- The upper extremity has a hemispherical head, a narrow neck and two processes extending from it. It articulates with the scapula (shoulder bone) to provide movement across the shoulder.
- The body is cylindrical overall and resembles a prism at the bottom.
- The lower extremity has two smooth articular surfaces trochlea and capitulum, two depressions or fossae that make up the elbow joint and two epicondyles or projections.
- The capitulum and trochlea articulate with radius and ulna, respectively.
- The two depressions of the fossae receive projections from the ulna bone.
- The epicondyles that are present on either side of the bones are the site of attachment of muscles of the forearm and fingers.
Radius and Ulna
- The humerus is present on the upper arm, while the radius and ulna are shorter bones that constitute the forearm.
- Radius is situated towards the side of the thumb and ulna on the opposite side.
- The ulna forms a true hinge joint with the elbow that provides extension and flexion movement. It also articulates with the wrist bones.
- The radius is a bone that has a smooth concave surface and articulates with the capitulum or head of the humerus. It articulates with the ulna on the side surfaces.
- The radius and ulna bones run parallel to each other. The ulna is longer than the radius but radius is thicker.
This sums up the bones of the arm. Keep visiting BYJU’S Biology for more exciting information.
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