Wikis embed information about authors, tags, hyperlinks and other metadata into the information they create. Wiki functions use this metadata to provide pointers which allow users to track down, or be informed of, the information they need. In this paper we provide a firm theoretical conceptualization for this type of activity by showing how this metadata provides a digital foundation for a Transactive Memory System (TMS). TMS is a construct from group psychology which defines directory-based knowledge sharing processes to explain the phenomenon of "group mind". We analyzed the functions and data of two leading Wiki products to understand where and how they support the TMS. We then modeled and extracted data from these products into a network analysis product. The results confirmed that Wikis are a TMS in digital form. Network analysis highlights its characteristics as a "knowledge map", suggesting useful extensions to the internal "TMS" functions of Wikis.