📝 STANDARD DESCRIPTION:
Weight-bearing column.
Ox Standard:
- Fused bones (No pronation/supination).
- Ulna is complete (reaches carpus).
- 2 Interosseous spaces (Proximal & Distal).
- Lateral Styloid process belongs to ULNA.
📚 DETAILED DESCRIPTION:
RADIUS & ULNA — BONES OF THE FOREARM (ANTEBRACHIUM)
The forearm of the ox is a fused, weight-bearing column. The radius is the larger weight-bearer; the ulna is reduced but COMPLETE (extends from olecranon to carpus, unlike horse where its distal half is vestigial).
RADIUS — main weight-bearer:
Proximal end:
• Head (Fovea capitis radii) — concave articular surface for capitulum of humerus; saddle-shaped.
• Radial Tuberosity — medial, just below head; insertion of biceps brachii.
• Neck — slight constriction.
Shaft:
• Slightly curved cranially.
• Cranial border (sharp) = palpable subcutaneously — fracture site.
Distal end:
• Trochlea radii — articular surface for proximal carpal row.
• Medial Styloid Process — bony bump on medial side; in OX the lateral styloid is part of ULNA.
ULNA — reduced but functional:
Proximal end:
• Olecranon — large beak-like projection forming the 'point of the elbow'; insertion of triceps brachii.
• Anconeal Process — projects forward from olecranon; locks into olecranon fossa during full extension.
• Trochlear Notch (Semilunar) — concave articular surface that grips the trochlea of humerus.
• Coronoid Processes — medial + lateral — articulate with radius.
Shaft: Lies caudal to radius; fused with it.
Distal end:
• Lateral Styloid Process — in OX, this is part of ULNA (in horse it belongs to radius!).
RELATIONSHIP IN OX:
• Radius and ulna are FUSED at proximal + distal ends, with 2 interosseous spaces (proximal + distal) closed by interosseous membrane.
• NO pronation / supination — the cursorial design locks the limb in pronation as a rigid column for forward locomotion (energy-efficient running).
UG MEMORY: 'Ox = fused, complete ulna, 2 spaces, lateral styloid = ulna. Horse = fused, ulna shaft fades, 1 space, lateral styloid = radius. Dog = SEPARATE, mobile, full pronation/supination.'
// COMPARATIVE ANALYSIS
| HORSE |
Ulna fuses mid-shaft (Distal half is vestigial). Lateral Styloid belongs to RADIUS. Only 1 proximal space. |
| DOG |
Separate bones. Mobile (allows pronation). Ulna has trochlear notch. |
| FOWL |
Ulna is larger than Radius. 'Quill Knobs' present on Ulna for feather attachment. |
CLINICAL RELEVANCE
Fractures: In horses, ulnar fractures usually involve the olecranon (dropped elbow) as the distal ulna is fused.
