39. 瀬戸内海産化石象に生じた齒牙腫に就て

抄録

The Specimen, a fragment of the right horizontal ramus of the mandible containing the first, second, and third molars, was dredged from the sea bottom Off the Island of Kotuti, Kagawa Prefecture in January 1933.It is now preserved at Waseda University, Tokyo.
The mandible is broken at the anterior margin of the first molar, the ascending ramus and the inner and lower sides of the horizontal ramus being also damaged.
Palaeopathologically speaking, a number of intresting features are observed in this specimen. First, a compound odontoma of the first and second molars has taken place, which is a benign tumor derived from an abnormal arrangement of dentine, enamel, and cementum and a sporadic calcification in tooth development. Second, a great hypertrophy of the right ramus has happened, which has given rise to a bulbous appearance to the jaw.
Third, the concavity of the diseased molar is greater than that of a normal molar. Fourth, the breadth of the former is one-and-a-half times that of the normal. And fifth, the enamel figure on the friction surface of the anomalous molar is irregular as shown in the plate. The third molar, which now contains the anterior talon and twelve ridges, has lost 4-8 ridges and the posterior talon. Its grinding had not yet begun. The maximum length of its crown is 180mm., and its width at the sixth ridge 60mm. The height of the crown is 128mm. at the fifth ridge, and 132mm. at the tenth. The frequency of ridges in a standard length of 100mm. is 6.5.
For reasons given above it is almost impossible to determine its specific name, but the writers believe that it may belong to Palaeoloxodon namadicus (FALCONER and CAUTLEY), the well known Pleistocene elephant.
Finally the writers wish to express their thanks to Professor Tosikazu Tokoro, Nippon Dental College, for dental information received.