Educational resource developed at the Veterinary Anatomy Section, ICAR-Indian Veterinary Research Institute (ICAR-IVRI), Bareilly.
📝 STANDARD DESCRIPTION:
Type: Intrinsic, Brachial (Extensor)
Heads: Long (scapula), Lateral (humerus), Medial (humerus), Accessory (neck of humerus)
Insertion: Olecranon tuber of ulna
Function: Extends elbow (primary weight-bearing extensor); long head flexes shoulder.
📚 DETAILED DESCRIPTION:
THE ANTI-GRAVITY EXTENSOR
The primary extensor of the elbow joint, essential for weight-bearing. Distinguished by possessing four heads in ox (same as dogs; vs. three in humans).
FOUR-HEADED ARCHITECTURE:
• Long Head (Caput Longum): Largest head; originates from caudal scapular border (biarticular—flexes shoulder, extends elbow)
• Lateral Head (Caput Laterale): Originates from lateral humeral shaft (tricipital line)
• Medial Head (Caput Mediale): Originates from medial humeral shaft (crest of lesser tubercle region)
• Accessory Head (Caput Accessorium): Unique to ruminants and carnivores (absent in horses/humans); originates from caudal aspect of neck of humerus; lies between lateral and medial heads—provides additional mass for heavy weight extension
MECHANICAL ADVANTAGE: All heads converge on the massive olecranon tuber of the ulna, providing a long lever arm for powerful elbow extension against ground reaction forces.
RADIAL NERVE DEPENDENCY: Solely innervated by the radial nerve. High radial nerve paralysis results in complete triceps failure and 'dropped elbow'—inability to bear weight.
CLINICAL EXAMINATION: Triceps tone maintains the elbow in extension during standing; loss of this tone is the immediate sign of radial nerve injury proximal to the elbow.
// COMPARATIVE ANALYSIS
| DOG |
Four heads (including accessory head); olecranon smaller relative to body. |
| HORSE |
Three heads; different split of lateral and medial heads. |
CLINICAL RELEVANCE
Capped Elbow (Olecranon Bursitis): Subcutaneous bursa over olecranon becomes inflamed from trauma (lying on hard surfaces). Radial Paralysis: Loss of triceps tone causes 'dropped elbow' and inability to support weight; most critical muscle for standing.
