The Foundational Model of Anatomy ontology contains approximately 75,000 classes and over 120,000 terms; over 2.1 million relationship instances from over 168 relationship types link the FMA’s classes into a coherent symbolic model. The FMA is one of the largest computer-based knowledge sources in the biomedical sciences.

The most comprehensive component of the FMA is the Anatomy taxonomy (At). The dominant class in the At is Anatomical Structure. Anatomical structures include all material objects generated by the coordinated expression of groups of the organism’s own structural genes. Thus, they include biological macromolecules, cells and their parts, portions of tissues, organs and their parts, as well as organ systems and body parts (body regions).

Macroscopic anatomical structures are most comprehensively represented, whereas biological molecules have been entered mainly to illustrate the structural continuum from major body parts, such as the thorax, to biological macromolecules, such as myosin.

Portions of body substances, such as blood, CSF, intercellular matrix, and cytoplasm, are defined in terms of their relationship to anatomical structures, and so are spaces, surfaces, lines and points that are associated with anatomical structures.

An objective of Foundational Model Explorer/Conducted Tour is to give an appreciation of the classes that subsume all these diverse classes within a continuous taxonomy.

Traditional sources do not include such a comprehensive taxonomy and do not explicitly define classes or types. Therefore we had to propose and define a number of classes or types of anatomical entities in the FMA for which there are no precedents in the traditional literature. There is an increasing correspondence between the FMA and traditional sources as one proceeds from the root of the At (Anatomical entity) toward the leaf classes of the FMA (e.g., heart, hepatocyte). For example, the FMA contains essentially all the terms of Terminologia Anatomica with an appropriate record of their derivation from this source.