The presentation concerns the evaluation of the anatomical plausibility of vocal tract shapes calculated by means of an analytical formant-to-area map. A constraint that requests that the jerk of the evolving model parameters is minimal is used to select a single solution among the infinitely many area functions that are compatible with the observed formant frequencies. A similarity measure between observed and inferred cross-sections has been computed to express the plausibility of the recovered shapes quantitatively. The test corpus has comprised observed area functions and formant frequencies of ten French vowels sustained by two male and two female speakers. Results show that vowel qualities involving double articulations have been the most likely to give rise to large dissimilarities between acoustically inferred and measured vocal tract cross-sections.