Transversal views of three-dimensional reconstruction of the posterior part of the skulls of A. Helminthophis flavoterminatus (AMNH R 59407); B. Helminthophis frontalis (MCZ R-55117); and C. Helminthophis praeocularis (AMNH R 38125), showing the contribution of the supraoccipital to the internal sidewall of the neurocranium in H. frontalis and H. praeocularis. Scale bars: 1 mm. Anatomical abbreviations: bo, basioccipital; p, parietal; ooc, otico-occipital (fused prootic + opisthotic + exoccipital); q, quadrate; rp, retroarticular process; so, supraoccipital.