A Morphological Study on the Cheek Tooth of Japanese Wild Boar (Sus scrofa leucomystax)

A morphological study was carried out on the cheek tooth of wild boar captured at Fukuoka and Yamaguchi prefectures. The materials available for this investigation consisted of a total of 78 cases, maxilla 37 (male 22, female 15), mandible 41 (male 24, female 17). The results obtained were summarized as follows. 1. The cheek teeth consisted of the four anterior, the three posterior cheek teeth, and the total of them were twenty-eight, indicating mammalian complete dentition. They were bunodont teeth with cone-shaped cusps, simultaneously brachyodont with short crown. 2. The 1st anterior cheek teeth which have been regarded as monophyodont without having any predecessors in these days, were variable in crown pattern and root shape, and they were frequently absent. The lacking rate of them was 71.8% in mandible, 17.4% in maxilla, and there was observed the differences of significance between both jaws clearly. 3. The cingulum appeared in the lingual side of maxillary anterior cheek teeth developed so well as the distal ones. It seemed that a small cusp which was adjacent to the cingulum was derived from the cingulum in their appearance. The buccal fossa appeared in mandibular anterior cheek teeth deepened so fully as the distal ones. 4. The maxillary 4th anterior cheek tooth presenting a triangular shape in appearance of the occlusal surface had three cusps of the paracone, metacone and protocone, which might be a primitive type, and assumed a tendency of molarization. 5. The 1st and 2nd posterior cheek teeth of both jaws had a four-cusped pattern respectively. Out of the mandibular cusp pattern, the hypoconulid developed well, while the paraconid disappeared almost, showing strong sign of reduction. 6. The mesiodistal diameter was the longest in the mandibular 3rd posterior cheek tooth, whose talonid was well grown just like heel-shape on the distal end. The buccolingual diameter in the maxillary 3rd posterior check tooth was the longest in the maxilla. 7. The tuberculum molare was found in mesiobuccal and distolingual side of the maxillary 2nd posterior cheek tooth, furthermore in the buccal side of the maxillary 3rd posterior one. 8. The occlusal spine appeared more in the lingual than in the buccal side of the maxillary teeth. And in the mandibular ones, it appeared more in the buccal side. 9. The parastyle and buccal ridge were observed markedly in the mesiobuccal side of the maxillary 4th anterior cheek tooth, therefore it seems that the appearance frequency of style has closely relation with that of ridge. 10. There was observed very markedly the central ridge of occlusal surface in the majority (97%) of the maxillary 4th anterior cheek tooth. 11. The variety of the mesiodistal diameter in maxillary cheek teeth was so marked as the distal one. In the mandible, that of anterior 1st one was the most variable and that of posterior 3rd one succeeded. There was observed the sexual difference in the buccolingual diameter of mesial side of maxillary 1st anterior one and of distal side of the mandibular 2nd and 3rd anterior ones respectively. 12. Considering the relative size of talon (-id) to the crown mesiodistal diameter in the posterior cheek teeth, the 3rd posterior one of each jaw was the largest, the maxillary one 42%, the mandibular one 46%. 13. The cheek teeth grew so complex as the distal ones. As concerns this, the author guessed as follows from viewpoint of the evolution of tooth. In the anterior cheek teeth, it speculated that the differentiation has happened first from the mesial tooth, and the diminution has arised from similarly the mesial in later stage, in the posterior cheek teeth, the differentiation the distal, and the diminution the distal in the same way.