Observations were made on high resolution radiographs of foetal sheep, from ewes slaughtered at 7-day intervals from 34 to 55 days after mating, to examine the onset of ossification of some of the major components of the axial and appendicular skeleton. There were 83 foetuses measured, retrieved from 24 Finnish Landrace × Polled Dorset Horn ewes mated to Suffolk rams. The litters comprised five sets of twins, eight of triplets, seven of quadruplets, three of quintuplets and one set of sextuplets.

Half of the ewes were subjected to a 50% reduction in food on the 28th day of gestation, but this was considered not to have affected skeletal growth and development.

There were major changes in skeletal mineralization from one slaughter date to the next, particularly between 34 days, when no skeletal elements were detectable, and 41 days, when components of the skull, thorax, fore and hindlimbs were clearly seen. There were some differences in the number of primary centres present both within and between litters of the same gestational age. The mineralized shaft of the fibula was seen in 30/35 of the foetuses at 41 days, but only in 9/25 at 55 days; other transient centres were also observed.

Changes in the linear dimensions of six limb bones were measured and the mean values are presented in tabular form.