Anatomical variations are categorized into three types including morphometric (size or shape), consistency (present or absent), and spatial (proximal/distal or right/left).
[2] Anatomical variations are mainly caused by genetics and may vary considerably between different populations.
[2] Knowledge of anatomical variations is important in order to distinguish them from pathological conditions.
[4] Some variations are found in different species such as polydactyly, having more than the usual number of digits.
[5] The sternalis muscle is a variant that lies in front of the pectoralis major and may show up on a mammogram.