In 1966, a separate register was opened for the breed. In fact, in the mid-1990s, the popularity of the Rottweiler reached an all-time high with it being the most registered dog by the American Kennel Club. In 2017, the American Kennel Club ranked the Rottweiler as the eighth-most popular pure-breed in the United States. In 2017, the American Kennel Club ranked the Rottweiler as the eighth-most popular pure-breed in the United States. The skull is of medium length, relatively broad between the ears. The forehead line is moderately arched as seen from the side, with the occipital bone well developed without being conspicuous. Frontal groove not too deep. When seen from behind, the rear legs are straight and not too close together. When standing free, obtuse angles are formed between the dog's upper thigh and the hip bone, the upper thigh and the lower thigh, and the lower thigh and metatarsal. The upper thigh is moderately long, broad and strongly muscled.