Overview
The horse has eighteen pairs of ribs (costae), one for each thoracic vertebra. Each rib has a dorsal bony part and a ventral costal cartilage. The first eight pairs are sternal (true) ribs: their cartilage articulates directly with the sternum. The last ten are asternal (false) ribs: their cartilages join that of the rib in front and form the long, very oblique costal arch (arcus costalis). The first ribs are short and almost straight, covered by the scapula and the muscles of the thoracic limb; the middle ones are the longest and widest.
Key features
- Head (caput costae): articulates with the costal foveae of two consecutive vertebrae.
- Neck and tubercle: the tubercle articulates with the transverse process of the vertebra of the same number.
- Body: long and curved; the intercostal vein, artery and nerve run along its caudal border.
- Costochondral junction: between the bony part and the cartilage; in the sternal ribs the cartilages articulate with the sternum by synovial joints.
- Thorax and abdomen: the diaphragm attaches far cranially, so the last ribs cover abdominal organs: the stomach and spleen on the left, the liver, the base of the caecum and the duodenum on the right.
- Lung field: a triangle auscultated caudal to the triceps; its caudal border descends from the 16th intercostal space at the level of the tuber coxae, passes the 11th at the level of the shoulder joint and reaches the 6th at the level of the elbow.
Clinical relevance
- Rib fractures in newborn foals: common after birth, mainly in the cranial ribs and close to the costochondral junction. The fracture ends can injure the heart, lungs or great vessels, so they are examined by ultrasound.
- Thoracocentesis: performed in the ventral thorax, above the costochondral junction, in the 7th or 8th intercostal space, passing the needle along the cranial border of the rib to avoid the intercostal vessels.
- Rib resection: gives access to the thoracic cavity for surgery or for draining pleural abscesses.