Note this is only for rendering. See the 'marchingCubesSurface' example to see how to extract a surface (triangles) from a volume.
Adding an SoVolumeIsosurface node before an SoVolumeRender enables to display one or multiple isosurfaces.
A SoMaterial node specifies the color and transparency of each isosurface. Here, for example, opaque bones and transparent skin.
SoVolumeData, SoVolumeIsoSurface