Part-of relations are central to anatomy. However, the definition, formalisation and use of part-of in anatomy ontologies is problematic. This paper surveys existing formal approaches, as well as the use of part-of in the Open Biological Ontologies (OBO) anatomies of model species. Based on this analysis, we propose a minimal ontology for anatomy which is expressed in the Semantic Web languages RDFS and OWL-Full. The paper concludes with a description of the context of this work in capturing cross-species tissue homologies and analogies.