Observations on the anatomy of mammary glands in two species of conilurine rodent (Muridae: Hydromyinae) and in an opossum (Marsupialia: Didelphidae).

Abstract

The pups of Pseudomys nanus and P. australis are attached to their mothers' teats for extended periods of time, analogous to the situation encountered in pouchless marsupials. The structures in the mammary glands involved in facilitating prolonged attachment are different in the two rodent species and both kinds are different from those in marsupial glands including those of Monodelphis domestica, the subject of the present study. In P. nanus, the teats are anchored to postero-ventrally directed, tubular diverticula of the body wall. In P. australis there are no diverticula. However, support for the mammary glands and teats is afforded by the body wall, in the form of two well-developed fan-shaped muscles dorsal to the mammary glands in conjunction with a broad lamina of connective tissue, smooth and striated muscle situated between the skin of the belly and the mammary glands. In M. domestica, the teats are anchored to swathes of striated voluntary muscle, derived from the ilio-marsupialis muscles which pass ventrally through the secretory parenchyma to be inserted onto the bases of the teats. Since this musculature has not been observed in the mammary glands of any eutherians so far studied, nor in those of Monotremata, it is put that it is a character unique to the Marsupialia.