THE EFFECTS OF THYROXIN AND THIOURACIL ON THE TIME OF APPEARANCE OF OSSIFICATION CENTERS OF RAT FETUSES

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Abstract
The time of appearance of the ossification centers studied was not significantly altered in the 16-day-old rat fetuses the mothers of which were injected daily with 1 mg. of crystalline thyroxin from either the 6th day or the 16th day of pregnancy. The time of appearance of the same ossification centers was delayed in the 16-day-old rat fetuses the mothers of which were fed on a diet containing 0.2 to 0.4% thiouracil, a goitrogenic drug, from date of pregnancy. Evidently the thyroid gland has a role in influencing the time of appearance (differentiation) of the ossification centers of membrane bones and primary endo-chondral bones. The thyroid hormone from the maternal thyroid gland may be essential for normal differentiation of the observed ossification centers appearing in 16-day-old rat fetuses.