Some observations on the morphology of the bovine teat canal (Ductus papillaris mammae).

After reviewing traditional and present day concepts of the mechanism by which the external orifice of the teat canal control the outflow of milk and the entry of bacteria etc. into the cavities of the mammary gland, this paper reports on the results of electron microscopic and other studies of the teat tip. This leads to the conclusion that the concept of a sphincter surrounding the teat canal should be substituted by one of a multi-spiralled, net-like integrated musculo-elastic system. This system may facilitate automatic closing and opening of the teat canal depending on the state of its major functional elements, namely (i) elastic fibres for passive closure under normal conditions (ii) smooth muscle fibres augmenting the former and (iii) the level of the intra-cisternal milk pressure. This closure is enhanced by soft teat canal keratin.