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The humerus (/ ˈ h juː m ər ə s /; pl.: humeri) is a long bone in the arm that runs from the shoulder to the elbow.It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections.
The ulna or ulnar bone (pl.: ulnae or ulnas) [3] is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the radius, the forearm's other long bone. Longer and thinner than the radius, the ulna is considered to be the smaller long bone of the lower arm.
The appendicular skeleton forms during development from cartilage, by the process of endochondral ossification. The appendicular skeleton is divided into six major regions: Shoulder girdle (4 bones) - Left and right clavicle (2) and scapula (2). Arms and forearms (6 bones) - Left and right humerus (2) (arm), ulna (2) and radius (2) (forearm).
The olecranon is situated at the proximal end of the ulna, one of the two bones in the forearm. [1] When the hand faces forward the olecranon faces towards the back (posteriorly). It is bent forward at the summit so as to present a prominent lip which is received into the olecranon fossa of the humerus during extension of the forearm.
Diagram showing stages of endochondral ossification. Endochondral ossification is the formation of long bones and other bones. This requires a hyaline cartilage precursor. There are two centers of ossification for endochondral ossification. The primary center. In long bones, bone tissue first appears in the diaphysis (middle of shaft).
X-ray showing osteophytes of spondylosis of the lumbar spine. A range of bone-formation processes are associated with aging, degeneration, mechanical instability, and disease (such as diffuse idiopathic skeletal hyperostosis).
The styloid process of the ulna projects from the medial and back part of the ulna. It descends a little lower than the head. The head is separated from the styloid process by a depression for the attachment of the apex of the triangular articular disk, and behind, by a shallow groove for the tendon of the extensor carpi ulnaris muscle.
The distal radioulnar joint (DRUJ) is a pivot joint located between the distal ends of the radius and ulna, which make up the forearm. Formed by the head of the ulna and the ulnar notch of the radius, the DRUJ is separated from the radiocarpal (wrist) joint by an articular disk lying between the radius and the styloid process of the ulna.