A radiographic study of development of the appendicular skeleton in the fetal pig.

In this study litters or groups of fetuses and piglets were taken at approximately 5 day internals from the 35th day of gestation to one month after birth and radiographs were prepared of their appendicular skeletons. A total of 502 fetuses and piglets from 49 litters or groups were used. From the radiographs the lengths of calcified diaphyses (humerus, radius, ulna, metacarpals III & IV, femur, tibia and metatarsals III & IV) were measured and the numbers of ossification centres were counted. The times of appearance and chronological order of the individual ossification centres in the limbs were also studied and a detailed sequence schedule is presented. Collected data were analysed statistically and mean development curves are given for each variable. Where applicable tolerance limits defining the boundaries within which 95% of values for normal individuals should fall are also expressed. Diaphyseal length was in all cases found to be a linear function of age and could be accurately expressed in terms of regression equations. The relationship between number of ossification centres and age was, however, complex and curvilinear but a graph expressing this relationship could be drawn by eye because of the very close relationship between the 2 factors. Sex differences in the skeletal parameters were small and not statistically significant though ossification was slightly faster in fernales than in males. It is concluded that this radiographic technique together with the normal developmental standards derived herein may be of value not only for accurate assessment of age in pig fetuses but also as a basis for comparison in cases where abnormal fetal development is suspected.