Results of a study designed to determine the effectiveness of implementing three-dimensional (3D) stereo images of a human skull in an undergraduate human anatomy online laboratory were gathered and analysed. Mental model theory and its applications to 3D relationships are discussed along with the research results. Quantitative results on 62 pairs were analysed using a doubly-multivariate analysis of variance repeated measures design. Results revealed statistically significant differences in group means for the main effect of treatment groups 2D and 3D and for the variables of Identification and Relationship with the 3D group outperforming the 2D group on both dependent variables.