Fig. 3

a Fetal rat vertebral column double stained with Alizarin red S and Alcian blue. (A) The control shows well-ossified vertebral centra; parts of the neural arches of atlas (at); axis (ax); the remaining cervical vertebrae (cv); the thoracic (tv), lumbar (lv), and sacral (sv) vertebrae; and the first one-third of the caudal vertebrae (ca.v). (B) The fetal rat vertebral column maternally treated with low dose of progesterone (1.8 mg/200 g bw) shows incomplete ossification all over the vertebral column with incomplete ossification of vertebral centra in cv, tv, lv, and sv. (C) The fetal rat vertebral column maternally treated with high-dose progesterone (3.6 mg/200 g bw) shows more pronounced incomplete ossification all over the vertebral column with unossified vertebral centra in cv, tv, lv, and sv. Also, unossified caudal vertebrae are observed. b The fetal rat sternum double stained with Alizarin red S and Alcian blue. (A) The control shows six fully ossified sternebrae (st) and cartilaginous sternal portions of the ribs (rb), free ribs (frb), manubrium (ma), and xiphoid process (xp), which also shows that the cartilage-ossification ratio of the body of the ribs increased caudally as descending. (B) The fetal rat sternum maternally treated with low-dose progesterone (1.8 mg/200 g bw) exhibited less pronounced incomplete ossification of the ribs and manubrium. (C) The fetal rat sternum maternally treated with high-dose progesterone (3.6 mg/200 g bw) shows more pronounced incomplete ossification of the sternebrae (st) with unossified manibrum. Also, xp shows incomplete ossification