The Boxer is a medium to large, short-haired breed of dog, developed in Germany. This group is a category of solidly built, large dog breeds that all descend from the same common ancestor, the large shepherd dog known as a Molossus. The Boxer is a member of the Working Group. Leading health issues to which Boxers are prone include cancers, heart conditions such as aortic stenosis and arrhythmogenic right ventricular cardiomyopathy (the so-called 'Boxer cardiomyopathy'), hypothyroidism, hip dysplasia, and degenerative myelopathy and epilepsy; other conditions that may be seen are gastric dilatation volvulus (also known as bloat), intestinal problems, and allergies (although these may be more related to diet than breed). Entropion, a malformation of the eyelid requiring surgical correction, is occasionally seen, and some lines have a tendency toward spondylosis deformans, a fusing of the spine, or dystocia. Care must be taken not to over-exercise young dogs, as this may damage growing bones; however, once mature, Boxers can be excellent jogging or running companions.