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The head of the radius has a cylindrical form, and on its upper surface is a shallow cup or fovea for articulation with the capitulum of the humerus.The circumference of the head is smooth; it is broad medially where it articulates with the radial notch of the ulna, narrow in the rest of its extent, which is embraced by the annular ligament.
The head of the radius is wider than the bone's neck, and, because the annular ligament embraces both, the radial head is "trapped" inside the ligament which thus acts to prevent distal displacement of the radius. [4] It helps to stabilise the proximal radial head, [6] and the radioulnar joint. [7]
The capitate is the largest carpal bone found within the hand. [2] The capitate is found within the distal row of carpal bones. The capitate lies directly adjacent to the metacarpal of the ring finger on its distal surface, has the hamate on its ulnar surface and trapezoid on its radial surface, and abuts the lunate and scaphoid proximally.
The third metacarpal bone (metacarpal bone of the middle finger) is a little smaller than the second.. The dorsal aspect of its base presents on its radial side a pyramidal eminence, the styloid process, which extends upward behind the capitate; immediately distal to this is a rough surface for the attachment of the extensor carpi radialis brevis muscle.
The ring metacarpal is somewhat more mobile while the fifth metacarpal is semi-independent. [ 1 ] Each metacarpal bone consists of a body or shaft, and two extremities; the head at the distal or digital end (near the fingers), and the base at the proximal or carpal end (close to the wrist).
The fourth metacarpal bone (metacarpal bone of the ring finger) is shorter and smaller than the third. The base is small and quadrilateral; its superior surface presents two facets, a large one medially for articulation with the hamate , and a small one laterally for the capitate .
Examples: The thumb is on the radial side of the hand (the same as saying the lateral side); the ulnar side of the wrist is the side toward the little finger (medial side). Ventral and dorsal, which describe structures derived from the front (ventral) and back (dorsal) of the embryo, before limb rotation.
Bamboo sign; Banana sign; Bat wing appearance; Bear paw sign; Beveled edge sign; Bird of prey sign; Bite sign; Black pleura sign; Blade of grass sign (also known as Flame sign); Blumensaat's line