Articulatory approaches to speech synthesis typically model the vocal tract as a series of concatenated tubes whose cross-sectional areas are related by some heuristic to the midsagittal profile. While adequate for lower formants, accurate modeling of higher frequencies requires access to details of tract morphology. With this aim we describe in this paper a parameterization of MRI-derived volumes that permits recovery of characteristic cross-sectional shape from the midsagittal profile alone.