This dissertation is a study of the differing explanatory criteria used for the assessment of epistemic medical claims, particularly anatomical claims, in the work of Galen of Pergamum (129-c. 216 CE). It focuses on Galen's use of anatomy and anatomical exegesis to position himself in relation to the various medical sects or haireseis active in the Late Roman Empire. Consequent on the emergence of invasive anatomical investigations in the early Hellenistic period (3rd cent. BCE), the explanatory and therapeutic value of anatomical information came to be a defining characteristic of competing medical sects. The Empiricists, who, we are told, were reacting to what they believed was the theoretical promiscuity of other medical thinkers, took their name from their reliance on experience rather than theory, the latter a methodological commitment they attributed to other medical thinkers whom they grouped under the broad category of Dogmatists. This sensitivity to theoretical claims is apparent from the fact that the Empiricists eschewed anatomical dissections, on the grounds that they required analogical moves from structures in corpses to structures in living creatures. If Galen is to be taken at his word, by the second century CE, sectarian disputes between the medical sects had risen to a fever pitch. Galen, who was at pains to make a place for his own medical beliefs in this debate, stresses the need for explanatory theoretical accounts of the body and things relevant to its biological function but also insists that these theoretical accounts be based in empirical observations. One of the arguments he must overcome is the problem of anatomical analogy, raised by the Empiricists. Galen not only engages with this issue from an abstract point of view but, this dissertation argues, he engages with it through the narrative structure of his anatomical accounts throughout his work and especially in his procedural anatomical handbook, De Anatomicis Administrationibus. Historically, this treatise has either been ignored by scholars or studied as a technical treatise that lacks in artifice. This dissertation questions this approach and considers the argumentative role of Galen's anatomical exegesis in the debate over the explanatory value of anatomy in Greco-Roman medicine. It takes as one of its main focuses, Galen's accounts of elephantine anatomy. It argues that these accounts are governed by different norms of assertion, which do not place the same premium on accurate reporting of anatomical detail, from the surrounding anatomical narrative in De Anatomicis Administrationibus. To that end, it shows the need for a more nuanced reading of fachprosa, such as Galen's anatomical work, than these texts have historically received.