There is great variability in the shape and size of the skeleton of the different breeds of domestic dogs, the morphology of the skull being one of the most diverse characteristics of the canine, with brachycephalic, mesocephalic and dolichocephalic breeds, corresponding to short, medium and long skulls respectively. The formation of the brachycephalic skull is the result of early ankylosis of the craniofacial growth plates, resulting in a shortening of the cranial and facial axis of the skull. Some studies indicate that the size and appearance of the skull is closely related to the size and appearance of the long bones, as there is a positive correlation between the width and length of both structures. Consequently, in the present investigation we sought to evaluate whether there are differences in the percentages of growth plate closure in the proximal epiphysis of the ulna between brachycephalic and mesocephalic dogs.