This nomenclature was developed by Henry Fairfield Osborn in 1907 and is, although with many variations, the one that continues today.The positions of tooth features are described along four directions: mesial (forwards, towards the chin), distal (backwards, towards the jaw joint), lingual (inwards, towards the tongue), and buccal or labial (outwards, towards the cheek).Therians (marsupials and placentals) ancestrally have roughly triangular upper molars, with the apex pointing lingually (inwards) and the flat edge positioned labially (outwards).Three major cusps are almost always present: Other common features include: Therians ancestrally have lower molars which are longer from front-to-back than from side-to-side.The trigonid region at the front part of the molar is triangular, with three large cusps: The talonid region at the rear part of the molar has two to three relatively small cusps which define the rear rim of a low basin: Other common features include: These are a list of tooth features identified in the rodent family Cricetidae (hamsters, voles, New World mice and rats, etc.).
Cricetidae molar teeth nomenclature after Reig, 1977.
