On the homology of the incisor teeth in the rabbit (Oryctolagus cuniculus)

The homology of the rabbit incisors has remained controversial despite abundant phylogenetic, developmental and morphological research. In this study, development and morphology of the incisors were investigated by means of serial histological sections and by stereomicroscopy in 10 fetal, 25 juvenile and 3 adult New Zealand White rabbits. A vestigial and a major incisor develop in both the upper and lower jaw, while a diphyodont minor incisor is located caudal to the major incisor in the upper jaw. Additionally, a unique case of incisor polydonty in an adult wild rabbit was investigated. The left incisive bone of this case bore a large supernumerary medial incisor which had all characteristics of a typical atavistic expression of the vestigial primordium of the first incisor. From this case the concept was deduced that the major incisor in the rabbit is monophyodont and corresponds to the second incisor, while the minor incisor in the upper jaw represents the diphyodont third incisor.