Complex sentence: The round shape of the breast helps to limit the loss of maternal body heat, because milk production depends upon a higher-temperature environment for the proper, milk-production function of the mammary gland tissues, the lactiferous ducts.
Split into simpler sentences: The round shape of the breast helps to limit the loss of maternal body heat. Milk production depends upon a higher-temperature environment for the milk-production function of the mammary gland tissues, the lactiferous ducts.