Overview
The sternum forms the floor of the rib cage. In the cat it consists of eight sternebrae, joined by intersternebral cartilages that ossify with age. The first is the manubrium and the last the xiphoid process.
Key features
- Manubrium (manubrium sterni): the first sternebra, elongated and slightly compressed laterally; it projects cranially at the thoracic inlet. The first pair of costal cartilages articulates with it, and the pectoral muscles and the sternocephalicus arise from it.
- Body (corpus sterni): sternebrae 2 to 7. The cartilages of pairs 2 to 9 articulate at the costal notches, at the level of the intersternebral spaces.
- Xiphoid process (processus xiphoideus): the last sternebra, extended by the xiphoid cartilage, a flexible plate on which the linea alba inserts.
- Muscles: the pectoral muscles arise from the ventral surface; the transversus thoracis from the dorsal surface.
Clinical relevance
- Pectus excavatum: dorsal displacement of the caudal sternebrae in kittens, which narrows the thorax; severe cases are corrected with external splints or surgery while the cartilages are still pliable.
- Median sternotomy: approach to the cranial mediastinum (for example to remove a thymoma) and to both hemithoraces.
- Radiography: lateral views show the sternebrae and the costal cartilages; mineralisation of these cartilages is a normal finding in older cats.