The term 'grammaticalization' refers to a process where new grammatical markers evolve from lexical items and derivative affixes, and the development on analogical processes of reanalysis and extension; productivity of use is essential for the grammatical status of a linguistic unit. The formal change is accompanied by semantic changes, especially metonymy and metaphor. The grammaticalization of body-part nouns is cross-linguistically widely documented, and this process can be based on two types of conceptualization models. The anthropomorphic model is based on the human body: the concepts of spatial orientation are expressed by human body-part names. The zoomorphic model is based on the structural template of the bodies of animals. In this study, both models are illustrated by examining the grammaticalization of the following body-part terms: Finnish/Estonian 'käsi' (hand) Fin. 'korva' ~ Est. 'kõrv' (ear), Fin.' kuve' (loins), Fin. 'kylki' ~ Est. 'külg'('flank), and Fin. 'rinta' (breast). The analysis is carried out in the framework of cognitive linguistics. The grammaticalization of ''''käsi' (hand' into a possession marker is based on the anthropomorphic model; I describe the process by investigating the basic concepts it expresses, following the extension of the usage through semantic verb classes, describing the range of possible possessors, and giving a characterization of the possesses. A group of nouns denoting side parts of the body has evolved into grams meaning 'beside' in Finnish and Estonian. This process is based on the zoomorphic model, but I show that the development is influenced by the general anthropocentricity of language use as well. In addition to the concrete spatial meaning, these grams have gained temporal, comitative, and metonymic and metaphoric relations of the meanings. (Dissertation Abstracts)