The term chordoma refers to a neoplasm arising from embryonic rests of the chorda dorsalis or notochord, which in its development more or less reproduces the structure of the primitive notochord. Chordomas arise in the craniospinal axis in certain definite locations, the selection of which can be explained on an embryologic basis. While they rarely metastasize, the clinical course is characterized by slow expansile enlargement with destruction of adjacent bone and compression of neural structures and by recurrences after operation. EMBRYOLOGY The embryology of the chorda dorsalis has been reviewed by others1and will be given briefly here. The notochord forms the primitive axial skeleton of all vertebrates, and in certain lower forms, such as the Amphioxus, it forms the sole axial skeleton. The structure is formed primarily by the proliferation of cells from the anterior end of the primitive streak. While some writers consider the chorda to be