The lists of tissues present at each Carnegie stage are organised on a part of basis and so give a simple hierarchy. Each tissue is thus only mentioned once.
The design of the hierarchy is the same as that used for the ontology of mouse developmental anatomy and is intended to be intuitive to follow.
The simple ontology includes all the basic tissues recognisable to an experienced histologist looking at H & E sections, together with links to notes and references. It does not include the more obscure tissues (e.g. the zonules of Zinn) or the constituent parts of most tissues.
The more detailed ontology excludes notes and references but does include the constituent parts of many tissues (e.g. several hundred tissues have associated mesenchyme as one of their parts). This ontology is designed for databases holding data associated with tissue at a fairly fine resolution (e.g. gene expression data) and is intended to be interoperable with GXD, the mouse gene expression database.