Appearance of ossification centers of the lower arm, wrist, lower leg, and ankle in immature orangutans and chimpanzees with an assessment of the relationship of ossification to dental development.

This study examines the appearance of the secondary ossification centers in the lower arms, wrists, lower legs, and ankles of a cross-sectional sample of 20 infant orangutans and chimpanzees (15 of known age). The number of tarsal and carpal centers is analyzed relative to the degree of M1 development and the weight of individual animals. Variation in the appearance of these ossification centers is discussed relative to these variables and others. In addition, a sequence of appearance is established for the carpal and tarsal ossification centers in the orangutan and data is presented on the status of these centers in a fetal and newborn gorilla. Study results indicate that 1) there is variation in the number of secondary epiphyses present in animals of similar ages; 2) tarsal ossification is completed prior to carpal ossification in the orangutan; 3) there are indications of a relationship between weight and the number of ossification centers present in animals of similar age; and 4) there appears to be no evidence of specific relationships between carpal and tarsal development and M1 development.