Deformed cow jawbone. Jawbone (mandible) of a cow affected by actinomycosis. Actinomycosis is a bacterial infection caused by Actinomyces sp. bacteria. In animals it is usually caused by Actinomyces bovis and is characterised by the formation of abscesses in the bones of the mouth. Here the abscesses have severely eroded the bone causing major deformity of the mandible. The condition is commonly known as 'lumpy jaw'. Photographed in the museum of the National Veterinary School of Alfort, Maisons-Alfort, France.