A rabbit skull showing arrangement of teeth.
The two upper incisors make impressions with four distinct arcs. This is because each tooth in the pair has a central groove and each side of the groove makes a small arc impression. The lower incisor pairs make very straight marks.
Photograph: By Klaus Rassinger und Gerhard Cammerer, Museum Wiesbaden (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons