ドブネズミの下顎臼歯における附加結節について On the Supplemental Tubercle of the Rattus norvegicus' Lower Molar.
A supplemental tubercle is often seen on the mesiobuccal part of the lamina on the lower molar of Rattus. We call this the mesiobuccal tubercle to distinguish it from the others. The main aim of this paper is to report on regional differences in its frequency of appearance on the mesiobuccal tubercle and to report on various supplemental tubercles on the lower molar of Rattus norvegicus. I. Regional difference: We have examined the regional difference of frequency of the appearance of the mesiobuccal tubercle in Rattus norvegicus, which were collected in the following four districts; Matsumoto City, Shiga Heights in Nagano Prefecture, Nagoya City and Fukuoka City. The most noticeable difference is found on the second lamina of the second molar. A quite significant difference is that the rate of frequency appearance on the right molar in Nagoya is 66.7%, which is far lower than the others; in Shiga Heights it is 91.7%, in Matsumoto City 95.1%, and in Fukuoka City 92.6%. On the second lamina of the third molar we recognize a regional difference, and especially the rate on the right molar in Nagoya, as well as that of the second lamina of the second molar, is much lower than the rate in the other three districts. II. Various supplemental tubercles which appear on the lower molar are as follows: 1) The supplemental tubercles found on the lingual surface between the first and the second lamina of the second molar. 2) The tubercle found on the distal surface of second lamina of the third molar. This tubercle is homologous to the posterior heel of the first and second molar and seems to be its remnant. 3) The tubercle found on the distobuccal of the first lamina of the first molar.
動物学雑誌 75(8), 227-235, 1966-08