This commercial model of Hall's "Alligator" is based on the principles outlined in the earlier prototype. (See Hall's prototype "Alligator" on this Web site.)
It was constructed to conform to Hall's "Conical" theory of mandibular movement. The theory stated that, if two equilateral (Bonwill) triangles were placed back to back, they would share the condylar (opening/closing) axis as a common base. The apex of the anterior triangle would be located at the incisal point and the apex of the posterior triangle would be located in the region of the external occipital protuberance. Finally, the posterior point would be the lateral rotation center of the mandible. However, the lateral rotation center of this manufactured instrument was located on a level with the occlusal plane and more adjustment features were added to accommodate differences in patients. Unlike the first version, this articulator was commercially available.
Dr. Edgar N. Starcke's articles in the Journal of Prosthodontics have more information on the history of articulators.