Overview
It fills the angle between the caudal border of the scapula and the humerus, and its outline shows under the skin behind the arm. It has three heads that end on the olecranon: long, lateral and medial. The long head is the bulkiest. Under its insertion tendon, on the olecranon, there is a subtendinous bursa; the subcutaneous olecranon bursa, at the point of the elbow, is the one that swells in "capped elbow".
Origin
- Long head (caput longum): caudal border of the scapula. It is 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.
Insertion
Olecranon tuber (tuber olecrani) of the ulna.
Action
Extends the elbow and holds it fixed when the horse bears weight. The long head also flexes the shoulder.
Innervation
Radial nerve (n. radialis).
Clinical relevance
- In radial nerve paralysis, from humeral fractures or compression during anaesthesia in lateral recumbency, the triceps is inactive: the elbow drops ("dropped elbow") and the horse cannot bear weight on the limb.
- In olecranon fractures, the pull of the triceps distracts the proximal fragment, so the horse cannot fix the elbow either. They are repaired with a tension band or a plate that neutralises that pull.
- Capped elbow (subcutaneous olecranon bursitis) occurs when the hoof or shoe strikes the point of the elbow as the horse lies down.