1. A method of producing 3-dimensional visualisations of digital representations of cross-sectional slices of a vertebrate animal or human body part includes the steps of: a) obtaining a first ordered series of slices of a portion of said body part in a first position; b) applying one or more filters to each of said digital representations of said first ordered series of slices to identify the skeletal portions of said body part; c) converting said first filtered series into a 3-dimensional representation of the skeleton of said body part in said first position; d) obtaining a second ordered series of slices of said portion of said body part in a second position different to said first position; e) applying one or more filters to each of said digital representations of said second ordered series of slices to identify the skeletal portions of said body part; f) converting said second filtered series into a 3-dimensional representation of the skeleton of said body part in said second position; g) combining said 3-dimensional representations to form a step frame animation having as many steps as there are ordered series of slices.