This article offers a novel perspective on the evolving identities and relationships of human medicine and veterinary medicine in England during the decades that followed the 1791 foundation of the London Veterinary College. Contrary to the impressions conveyed by both medical and veterinary historians, it reveals that veterinary medicine, as initially defined, taught and studied at the college, was not a domain apart from human medicine but rather was continuous with it. It then shows how this social, cultural, and epistemological continuity fractured over the period 1815 to 1835. Under the impetus of a movement for medical reform, veterinarians began to advance an alternative vision of their field as an autonomous, independent domain. They developed their own societies and journals and a uniquely veterinary epistemology that was rooted in the experiences of veterinary practice. In this way, "one medicine" became "two," and the professions began to assume their modern forms and relations.