The Welsh variety was small and nimble, domesticated and friendly, and also herded goats. When the English saw these dogs at the Birmingham market, they interbred them with their own variety of sheepdogs, producing a mixture of short- and long-haired varieties. After the industrial revolution, dog ownership became fashionable, and these early collies were believed to have been crossed with the Borzoi (Russian Wolfhound) to get a more 'noble' head (longer muzzle), which is today one of the true characteristics of the Rough Collie. This is light in relation to the rest of the body, and resembles a blunted wedge tapering smoothly from ears to black nose, with a distinct stop and parallel head planes. The muzzle is well rounded, and never square. It is not known conclusively if the Borzoi cross made it into the mainstream of the breed. Collie eye anomaly (CEA), a genetic disease which causes improper development of the eye and possible blindness, is a common ailment in the breed.