Bone Growth aud Development of Secondary Ossification Centers of Extremities in the Cynomolgus Monkey (Macaca fascicularis)

The development of so-called long bones in the extremity has been studied roentgenographically in forty-seven males and fifty-one females cynomolgus monkeys bred and reared at the National Institute of Health. The age of the females ranged from five months to eight years and nine months, and that of the males was from four months to seven years. In addition, the fetuses of six to twenty weeks of gestation age were examined for the time of appearance of ossification centers. As the biological parameters concerning body growth, the body weight and the bone length were measured and the secondary ossification centers were scrutinized and assessed the maturity process on the basis of the criteria that divided the state into eleven stages. Also the allometric analyses of body weight against bone length was conducted. Most of the secondary ossification centers except the proximal fibulal epiphysis appeared during the period from the prenatal stage (15-20 weeks of gestationage) to the postnatal one (several months of age). From four to five months of age, many ossification centers had developed to some extent. But, the appearance of proximal fibulal epiphysis was delayed and often lacking until 10 months of age in female and one year and three months of age in male. The earliest epiphyseal fusion was observed at the distal humeral epiphysis in both sexes. The latest epiphyseal fusion was observed at the distal ulnal epiphysis in both sexes and at the distal ulnal and radial epiphyses in female. From this study, the time of fusion was at five and three guarters years of age in females and at six and a half years of age in males. As a result, it is suggested that the estimation of animal's age might be put to practical use by introducing the assessing method that the score was given from the observation of the secondary ossification center.