(zoology) A theory of the development of mammalianmolar teeth. The primitive stage is that of simple cones, as in reptiles. The simple cone then developed a smaller cone in front and another behind, and then a cingulum, and the three cones became arranged in a triangle (the trigon or trigonid; this stage is called the tritubercular or trigonodont), the two smaller cusps having moved to the outer side in upper and to the inner in lower molars. The trigon being a cutting apparatus, an extension of the posterior part of the crown was developed in lower molars for crushing, and a smaller corresponding part appeared in upper molars. Another large cone then arose, usually from the cingulum. In more complex forms, smaller intermediate cusps appeared.
