Initial Development of the Mammary Gland Is Programmed by Embryonic Mesenchyme

The fetal development of the mammary gland is under both genetic and endocrine control. The initial development of the mammary bud is under control of embryonic mesenchyme (connective tissue). If mammary mesenchyme is transplanted to another area, mammary bud formation will occur at the site of transplantation. Although little is known about fetal mammary development, it is not thought to be driven by hor­mones. However, actively secreting mammary glands may be present at birth as a result of exogenous administration of certain hormones to the mother.