Articular surfaces

It is provided with two articular surfaces - one below, for the carpus

Carpus

In tetrapods, the carpus is the sole cluster of bones in the wrist between the radius and ulna and the metacarpus. The bones of the carpus do not belong to individual fingers , whereas those of the metacarpus do. The corresponding part of the foot is the tarsus...

, and another at the medial side, for the ulna

Ulna

The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...

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• The carpal articular surface is triangular, concave, smooth, and divided by a slight antero-posterior ridge into two parts. Of these, the lateral, triangular, articulates with the scaphoid bone
  Scaphoid bone
  The scaphoid bone is one of the carpal bones of the wrist. It is situated between the hand and forearm on the thumb-side of the wrist . The scaphoid bone is the largest bone of the proximal row of wrist bones, its long axis being from above downward, lateralward, and forward...
  
  ; the medial, quadrilateral, with the lunate bone
  Lunate bone
  The lunate bone is a carpal bone in the human hand that may be distinguished by its deep concavity and crescentic outline. It is situated in the center of the proximal row of the carpus region between the fore arm and hand...
  
  .

• The articular surface for the ulna is called the ulnar notch (sigmoid cavity) of the radius; it is narrow, concave, smooth, and articulates with the head of the ulna.

These two articular surfaces are separated by a prominent ridge, to which the base of the triangular articular disk is attached; this disk separates the wrist-joint from the distal radioulnar articulation.

Non-articular surfaces

This end of the bone has three non-articular surfaces - volar, dorsal, and lateral.

• The volar surface, rough and irregular, affords attachment to the volar radiocarpal ligament
  Volar radiocarpal ligament
  The palmar radiocarpal ligament is a broad membranous band, attached above to the anterior margin of the lower end of the radius, to its styloid process, and to the front of the lower end of the ulna; its fibers pass downward and medialward to be inserted into the volar surfaces of the scaphoid,...
  
  .

• The dorsal surface is convex, affords attachment to the dorsal radiocarpal ligament
  Dorsal radiocarpal ligament
  The dorsal radiocarpal ligament less thick and strong than the volar, is attached, above, to the posterior border of the lower end of the radius; its fibers are directed obliquely downward and medialward, and are fixed, below, to the dorsal surfaces of the navicular , lunate, and triangular, being...
  
  , and is marked by three grooves. Enumerated from the lateral side:
  • The first groove is broad, but shallow, and subdivided into two by a slight ridge; the lateral of these two transmits the tendon of the extensor carpi radialis longus muscle
    Extensor carpi radialis longus muscle
    Extensor carpi radialis longus is one of the five main muscles that control movements at the wrist. This muscle is quite long, starting on the lateral side of the humerus, and attaching to the base of the second metacarpal bone .-Function:As the name suggests, this muscle is an extensor at the...
    
    , the medial the tendon of the extensor carpi radialis brevis muscle
    Extensor carpi radialis brevis muscle
    The Extensor carpi radialis brevis is shorter and thicker than the extensor carpi radialis longus. The longus muscle can be found above the distal end of the Extensor carpi radialis brevis.-Origin and insertion:...
    
    .
  • The second is deep but narrow, and bounded laterally by a sharply defined ridge; it is directed obliquely from above downward and lateralward, and transmits the tendon of the extensor pollicis longus muscle
    Extensor pollicis longus muscle
    In human anatomy, the extensor pollicis longus is a skeletal muscle located dorsally on the forearm. It is much larger than the extensor pollicis brevis, the origin of which it partly covers, and acts to stretch the thumb together with this muscle....
    
    .
  • The third is broad, for the passage of the tendons of the Extensor indicis proprius
    Extensor indicis proprius
    -External links: - "Extensor Region of Forearm and Dorsum of Hand: Deep Muscles of Extensor Region"...
    
     and Extensor digitorum communis.

• The lateral surface is prolonged obliquely downward into a strong, conical projection, the styloid process, which gives attachment by its base to the tendon of the brachioradialis, and by its apex to the radial collateral ligament
  Radial collateral ligament
  Radial collateral ligament can refer to:* Radial collateral ligament * Radial collateral ligament * Radial collateral ligament...
  
   of the wrist-joint. The lateral surface of this process is marked by a flat groove, for the tendons of the abductor pollicis longus muscle and extensor pollicis brevis muscle.