Mammary gland gestation, serum progesterone remains at a stably high concentration so signaling through its receptor is continuously activated. As one of the transcribed genes, Wnts secreted from mammary epithelial cells act paracrinely to induce more neighboring cells' branching. When the lactiferous duct tree is almost ready, "leaves" alveoli are differentiated from luminal epithelial cells and added at the end of each branch. In late pregnancy and for the first few days after giving birth, colostrum is secreted. Milk secretion (lactation) begins a few days later due to reduction in circulating progesterone and the presence of another important hormone prolactin, which mediates
Saint Bathans mammal It was part of an assemblage of fossils recovered in Saint Bathans in 1978, in what would later be understood to be the Bannockburn Formation (Manuherikia Group), and first described in 2006. Like most small mammal fossils, the Saint Bathans mammal material is rather incomplete, with only a lower jaw fragment and femur being known. The lower jaw is toothless, though the presence of deep tooth sockets suggests that it was toothed in life and that the teeth were lost post-mortem. It bears a long fused mandibular symphysis, an evidently procumbent lower incisor, and five additional sockets that imply a