📝 STANDARD DESCRIPTION:
Robust, short, twisted long bone.
Ox Standard:
- Massive Greater Tubercle (overhangs groove).
- Intertubercular (Bicipital) Groove is undivided.
- Musculospiral groove is distinct.
- NO Supratrochlear foramen.
📚 DETAILED DESCRIPTION:
HUMERUS — BONE OF THE ARM (BRACHIUM)
A robust, short, twisted (helical) long bone forming the only bone of the upper arm. It bears the body weight transmitted from scapula → forearm.
PROXIMAL END (SHOULDER):
• Head (caput humeri) — large, smooth, hemispherical; articulates with glenoid cavity → shoulder joint (ball-and-socket, multiaxial).
• Neck — slight constriction below the head.
• Greater Tubercle (Tuberculum majus) — laterally placed; massive in ox, overhangs the bicipital groove. Insertion of supraspinatus + infraspinatus + teres minor + deep pectoral.
• Lesser Tubercle (Tuberculum minus) — medial, smaller; insertion of subscapularis + teres major + latissimus dorsi.
• Intertubercular (Bicipital) Groove — between the two tubercles; transmits the tendon of biceps brachii. Undivided in ox; divided by an intermediate tubercle in HORSE — the basis of the equine stay apparatus.
SHAFT (BODY):
• Cylindrical proximally, somewhat triangular distally.
• Deltoid Tuberosity — large bony prominence on the cranio-lateral surface; insertion of deltoid + brachiocephalicus.
• Tricipital Line / Crest — connects deltoid tuberosity to greater tubercle.
• Musculospiral Groove (Sulcus brachialis) — diagonal groove on caudo-lateral aspect; lodges the radial nerve + brachial artery branches. The radial nerve is highly vulnerable here in recumbent cattle ('downer cow' radial paralysis).
• Nutrient Foramen — usually on caudal surface of mid-shaft.
DISTAL END (ELBOW):
• Condyle of humerus — articular surface for forearm; has 2 parts:
– Trochlea (medial, larger) — pulley shape; articulates with ulna.
– Capitulum (lateral) — articulates with radius.
• Medial + Lateral Epicondyles — non-articular ridges above the condyle; origin of forearm muscles. The medial epicondyle (= 'flexor epicondyle') is the bovine 'funny bone' — ulnar nerve passes caudally.
• Olecranon Fossa — deep depression on caudal surface; receives anconeal process of ulna in extension.
• Coronoid (Radial) Fossa — smaller, on cranial surface; receives radius head in flexion.
• Supratrochlear Foramen — hole connecting olecranon and coronoid fossae; PRESENT in DOG; ABSENT in OX, HORSE, PIG (solid bone for weight support).
UG MEMORY: 'Head + 2 tubercles + groove proximally; condyle + 2 epicondyles + 2 fossae distally; spiral groove for radial nerve in mid-shaft.'
// COMPARATIVE ANALYSIS
| HORSE |
Intermediate Tubercle present (divides bicipital groove). Greater Tubercle forms 'Point of Shoulder'. |
| DOG |
Supratrochlear Foramen present (hole between condyles). Greater tubercle is lower than head. |
| PIG |
Greater tubercle almost closes the groove into a foramen. |
| FOWL |
Pneumatic bone (air-filled). Pectoral crest replaces deltoid tuberosity. |
CLINICAL RELEVANCE
Radial Nerve Paralysis: Vulnerable in the musculospiral groove. Causes dropped elbow and inability to extend the carpus.
