Overview
The sternum (sternum) forms the floor of the rib cage. In cattle it consists of seven sternebrae (sternebrae). The first is the manubrium, the following ones form the body and the last is the xiphoid process. Unlike the keel-shaped sternum of the horse, the bovine sternum is broad and flattened dorsoventrally and widens caudally.
Key features
- Manubrium (manubrium sterni): first sternebra, at the thoracic inlet; the first pair of ribs articulates with it. In cattle it does not fuse with the body: a true joint, the manubriosternal joint (articulatio manubriosternalis), connects them and allows some movement.
- Body (corpus sterni): the intermediate sternebrae, joined by cartilage that ossifies with age. The cartilages of the remaining sternal ribs articulate at the costal notches, level with the spaces between sternebrae.
- Xiphoid process (processus xiphoideus): last sternebra, extended by the xiphoid cartilage, a wide plate on which the linea alba inserts.
- Muscles: the pectoral muscles originate on the ventral surface; the transversus thoracis on the dorsal surface.
Clinical relevance
- Sternal recumbency: the normal resting position of the cow, lying on the sternum with the limbs folded. A downer cow should be kept in sternal recumbency, because prolonged lateral recumbency prevents eructation of rumen gas and favours bloat, regurgitation and aspiration pneumonia.
- Traumatic reticuloperitonitis: the reticulum rests on the xiphoid region, next to the diaphragm; firm pressure with a fist or a bar under the xiphoid causes pain and a grunt when a metallic foreign body has perforated its wall.
- Brisket oedema: in right-sided heart failure (traumatic pericarditis, high-altitude disease) subcutaneous oedema accumulates over the sternal region and in the intermandibular space.