Anatomy of the Ulna Bone

Upper Limb Bones

• Radial notch: a concave surface on the lateral side of the coronoid process that articulates with the head of the radius to form the superior radio-ulnar joint.
• Ulna body: triangular in the upper ¾ and cylindrical in the lower ¼.
• Lower end of ulna:
  • Head: small and rounded, articulating with the medial side of the lower end of the radius to form the inferior radio-ulnar joint.
  • Styloid process: projects medially and below the head.

Bones of the Hand

• 27 bones in total, consisting of:
  • Carpal bones: 8 in number, arranged in 2 rows (proximal and distal).
  • Metacarpal bones: 5 in number, one for each finger.
  • Phalanges: 14 in number, with 3 in each finger (proximal, middle, and distal) except the thumb, which has only 2 (proximal and distal).

Muscles of the Upper Limb

Muscles of the Shoulder Region

• 15 muscles divided into 3 groups:
  • Muscles of the pectoral region:
    • Pectoralis major: originates from the clavicle and sternum, inserts into the lateral lip of the bicipital groove of the humerus, and flexes and adducts the arm while medially rotating it.
    • Other muscles in this group include pectoralis minor, serratus anterior, and subclavius.

Muscles of the Hand

• Interossei:
  • 4 dorsal interossei muscles: occupy the intervals between the metacarpal bones and are bipenniform muscles.
  • 3 or 4 palmar interossei muscles: smaller and placed on the palmar surfaces of the metacarpal bones.
  • All interossei muscles are supplied by the ulnar nerve.
• Action of the interossei:
  • Palmar interossei: adduct the fingers to an imaginary line drawn longitudinally through the center of the middle finger.
  • Dorsal interossei: abduct the fingers from that line.

Nerve Supply

• Ulnar nerve (C.8 and T.1) is motor to 15 ½ muscles:
  • 1 ½ muscles in the front of the forearm.
  • 14 short muscles in the hand.
• Median nerve (C.5, 6, 7, 8, and T.1) is motor to 12 ½ muscles:
  • 6 ½ muscles in the front of the forearm.
  • 6 short muscles in the hand.

Muscles of the Forearm

• Anterior or flexor muscles: 8 in number, consisting of:
  • Superficial group: 5 muscles, including pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris, and flexor digitorum superficialis.
  • Deep group: 3 muscles, including flexor digitorum profundus, flexor pollicis longus, and pronator quadratus.