Program to transform mesh and offsets of this mesh in polylines which converge to the last offset (volume near 0). I called that veinization because it is like vein, not nerves nor venation. It requires Millepede plugin for isosurface calculation, Shrotest Walk and Mesh Edit. 

Polylines can be converted to spline and curvepiping applied like in the last image. 

Sort of medial axis are generated, not perfect :-( They are used to link shrinking zones

20140911_veinization_p.gh (correction of 2 bugs from march version)

Rabbit : Stanford Bunny from Stanford Computer Graphics Laboratory

Cow : model is provided courtesy of MPII by the AIM@SHAPE Shape Repository

Fertility : model is provided courtesy of UU by the AIM@SHAPE Shape Repository

Horse : model is provided courtesy of the AIM@SHAPE Shape Repository