📝 STANDARD DESCRIPTION:
Triangular flat bone (os planum).
Ox Standard:
- Spine is sinuous and divides lateral surface into 1:3 ratio (Supra:Infra).
- Acromion process is pointed and distinct.
- Subscapular fossa is shallow.
- Glenoid cavity is circular without a notch.
📚 DETAILED DESCRIPTION:
SCAPULA — THE SHOULDER BLADE
The scapula is a flat triangular bone (os planum) that forms the proximal part of the forelimb girdle. In domestic mammals it has NO bony attachment to the axial skeleton — it is suspended from the trunk by a muscular sling ('synsarcosis'), which lets it glide cranio-caudally to add length to the stride.
BORDERS (3):
• Cranial border — slightly convex; gives origin to supraspinatus.
• Caudal border — thicker; gives origin to teres major and the long head of triceps.
• Dorsal border — bears the scapular cartilage (cartilago scapulae) in large herbivores — adds 3-5 cm of attachment area.
ANGLES (3):
• Cranial angle — between cranial and dorsal borders.
• Caudal angle — between caudal and dorsal borders.
• Ventral angle (glenoid angle) — distal; bears the glenoid cavity.
SURFACES (2):
• Lateral (Costal-opposing) surface — divided by the scapular spine into:
– Supraspinous fossa (cranial — narrow in ox, ratio 1:3) for supraspinatus.
– Infraspinous fossa (caudal — wide) for infraspinatus.
• Medial (Costal) surface — has the subscapular fossa for subscapularis (shallow in ox; deep in horse).
KEY FEATURES:
• Spine of scapula — vertical ridge on lateral surface; sinuous (S-shaped) in ox; ends distally as the ACROMION in ox & dog (ABSENT in horse).
• Tuber spinae — thickening of the middle of the spine; very prominent in horse, replaces acromion.
• Glenoid cavity — shallow oval socket at ventral angle; receives the head of humerus → shoulder joint.
• Supraglenoid tubercle — small projection cranial to glenoid; origin of biceps brachii.
• Coracoid process — small medial projection of supraglenoid tubercle; origin of coracobrachialis.
• Scapular notch — at the base of the spine where the suprascapular nerve crosses (vulnerable site → 'Sweeney').
UG MEMORY HOOK: 'Triangular bone, 3 borders, 3 angles, 2 surfaces, 1 spine ending in acromion (in ox/dog) or tuber spinae (in horse).'
// COMPARATIVE ANALYSIS
| HORSE |
Acromion ABSENT. Spine fades distally. Prominent 'Tuber Spinae' present. Glenoid notch present. |
| DOG |
Acromion prominent with 'Hamate Process'. Spine high, 1:1 fossa ratio. |
| PIG |
Tuber spinae is very prominent and recurved caudally. |
| FOWL |
Saber-like blade. No spine/fossae. Parallel to vertebrae. |
CLINICAL RELEVANCE
Sweeney Shoulder (Horse): Atrophy of supra/infraspinatus muscles due to suprascapular nerve damage as it crosses the neck of the scapula.
