The concept of body plays an important role not only in language acquisition, but also in conceptualization of the world. From the perspective of empiricism and cognitive linguistics, the concept of embodiment is important in conceptualizing reality. The concept of body, however, is not fixed, but it changes in time. Sign system also transforms in time and the idea of semiosis catches the change accurately and properly. A group of words referring to body part shows the change in time and in their semantics very well. Somatism in language has been investigated in the research of metaphor and metonymy, but semantic extension of somatism cannot be described perfectly with the binary opposition of metaphor and metonymy. The alternative which is taken in this research is the trichotomy of signs by Charles S. Peirce. The trichotomy shows 10 types of sign classes and the 10 classes can be applied to the classification of semantic extension in somatism. The trichotomy explains delicate aspects of semantic extension in the diverse meanings of somatism. The purpose of the present research is to suggest a new way of explaining semantic relations among the meanings of a polysemous word. Another expectation would be the new explanation using the trichotomy applicable not only to linguistic phenomena, but to other semiotic occurrences as well.