Overview
In the dog it has four heads ending on the olecranon: long, lateral, medial and accessory. The model shows the first three; the accessory head is deep and hidden between them.
Origin
- Long head (caput longum): caudal border of the scapula. The only head that crosses the shoulder.
- Lateral head (caput laterale): tricipital line on the lateral surface of the proximal humerus.
- Medial head (caput mediale): medial surface of the humerus, in its proximal third.
Insertion
Olecranon tuber (tuber olecrani) of the ulna.
Action
Extends the elbow and supports body weight when standing. The long head also flexes the shoulder.
Innervation
Radial nerve (n. radialis).
Clinical relevance
Radial nerve injury prevents elbow extension: the dog cannot bear weight on the limb and drags it. The long head is an intramuscular injection site; the distal arm is avoided because the radial nerve lies close to the humerus there.