Triceps brachii muscle

The triceps brachii muscle is the muscle caudal to humerus and shoulder joint, that fills the triangle between the caudal border of the scapula, the humerus and the olecranon.

Its caudal border (margo tricipitalis) extends from the olecranon into the direction of the withers and is clearly visible under the skin in the live animal.

The triceps brachii possesse three heads of origin, and in the dog, adn additional accessory head, that terminates on a single distal insertion on the olecranon of ulna:

• Long head of triceps brachii:
  • Origin: Distolateral two-thirds of the caudal edge of the scapula, infraglenoid tubercle
  • Insertion: Olecranon of the ulna.
  • Action: Extension of the elbow joint, and especially for the long head, also flexion of shoulder joint
  • Nerve: Radialis.
• Lateral head of triceps brachii:
  • Origin: laterally on humerus: crest of the greater tubercle of the humerus, tricipital line, humeral crest in carnivores
  • Insertion: Olecranon of the ulna.
  • Action: Extension of the elbow joint.
  • Nerve: Radialis.
• Medial head of triceps brachii:
  • Origin: medially on humerus: caudal of tuberosity of teres major, crest of the lesser tubercle
  • Insertion: Olecranon of the ulna.
  • Action: Extension of the elbow joint.
  • Nerve: Radialis.
• Accessory head of the triceps brachii (in dogs):
  • Origin: proximal caudal part of the neck of the humerus.
  • Insertion: Olecranon of the ulna.
  • Action: Extension of the elbow joint.
  • Nerve: Radialis.