Many papers on Macaca fuscata (Japanese monkeys) have been published, but among them there is no paper which deals mainly with the eruption of their deciduous teeth. This report aims to present statistical results on the eruption age of the deciduous teeth in this species.The sample used for this study includes a total of 384 cases of observations on dental eruption, which were obtained from 76 wild and caged animals belonging to various troops (Table 1). Differences between groups and sexes were not considered for the analysis because sample sizes were not always sufficiently large, and concerning dental eruption, differences between sexes and habitats are less important than individual variations within groups. The age of the animals used for this study varies from day of birth to 12.5 month. The degree of erup- tion of a tooth crown was defined as the average eruption between corresponding left and right teeth.1) The sequence of tooth eruption The average eruption sequence is (i1, i1)→i2→i2→(c, , c', m1, m1)→m2→m2. Parentheses indicate that the eruption orders are variable between the bracketed teeth, and the arrow means that the tooth written before it always begins to erupt earlier than the following teeth. 2) The age of tooth eruptionStatistics and analyses of eruption age are complicated and, therefore, only a relatively simple statistical report is shown in Table 2. These results were based on the eruption of any portion of tooth crown.More detailed relationship between age and number of animals (expressed in percentages) which had each deciduous tooth is illustrated in Fig. 1. This figure contains not only results on the beginning of tooth eruption (dotted lines) which were calculated from Table 1, but also information on the eruption of at least about half (broken lines) and the whole (solid lines) of the tooth crown. There are fairly large individual variations in the age at which each of the teeth erupts. Table 3 is a tentatively made norm for eruption age, which covers around eighty percent of the individual variations docummented in our study.Among three species of macaques, M, fuscata, M. mulatta and M. fascicularis, it appears that the deciduous incisor erupts somewhat earlier in M, fuscata, while the deciduous second molar erupts somewhat earlier in M, mulatta, as seen in Table 4.
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