The creation of computer-animated human faces is a long-standing and challenging problem since the early 1970s. There are numerous approaches to facial animation, but to this day no general-purpose system exists that solves the problem in a manner satisfying the needs of all practical applications. An obvious approach to achieve generality is the simulation of the inner workings of a real face. The ultimate goal is to have the full range of conformation and expressiveness in the face emerge "naturally" through precise modeling of the anatomical structure and accurate simulation of tissue properties. This has so far only been realized in parts, and no current implementation catches all the intricacies of the human face. This text describes an approach for building and animating virtual head models with anatomical structure, animated in a physics-based manner by use of muscle contractions that in turn cause skin deformations.