📝 STANDARD DESCRIPTION:
Floor of thoracic cavity (breastbone).
Ox Standard:
- Made of 7 sternebrae.
- Three parts: Manubrium (cranial), Body (middle), Xiphoid process + cartilage (caudal).
- Shape: dorso-ventrally FLATTENED (boat-shaped).
- Manubrium projects cranially as 'Brisket' — palpable in front of forelimbs.
- 7 pairs of costal cartilages articulate on its sides.
📚 DETAILED DESCRIPTION:
THE FLOOR OF THE CHEST
The sternum is an unpaired bone forming the ventral floor of the thoracic cavity. It is segmented into bony pieces called sternebrae, joined by cartilage.
PARTS:
• Manubrium (Presternum): First sternebra. Projects forward as the brisket in cattle (a fatty, palpable point in front of the chest).
• Body (Mesosternum): Middle sternebrae (2nd-6th). Bears facets on its sides for the costal cartilages.
• Xiphoid Process + Cartilage (Metasternum): Last segment, ends in a flat cartilage plate (xiphoid cartilage).
SHAPE: In ruminants, the sternum is flat from above to below (boat-shaped); this gives them a wide, floor-like brisket. In horses it is compressed side-to-side (keeled), and in birds it forms a deep keel/carina for flight muscle attachment.
FUNCTION:
• Floor of thorax — protects heart from below.
• Anchor for costal cartilages of true (sternal) ribs.
• Origin for pectoral muscles (which attach the forelimb to the chest).
CLINICAL POINT: The brisket and xiphoid are surface landmarks. The xiphoid marks the caudal end of the thorax and the start of the diaphragm.
// COMPARATIVE ANALYSIS
| HORSE |
6-8 sternebrae. Compressed side-to-side (keeled). Has a ventral 'cariniform cartilage'. |
| DOG |
8 sternebrae. Cylindrical and rod-like. |
| PIG |
6 sternebrae. Manubrium pointed and projects forward. |
| FOWL |
Single large plate with deep ventral keel/CARINA for attachment of huge flight muscles (pectoralis & supracoracoideus). |
CLINICAL RELEVANCE
Brisket Disease (High-altitude disease, Cattle): Right-sided heart failure causes oedema (fluid swelling) in the brisket — visible as a sagging chest in front of the forelimbs.
Sternal recumbency: Normal resting position of cattle; weight rests on the wide flat sternum.
