Upon separating the hairs of the middle region of the back about a third
of the distance between the ears and the rump, one uncovers a prominent
gland, elliptical in outline, with long axis longitudinal and about 9
millimeters in length. The gland presents a roughened and granular
appearance, and fewer hairs grow upon it than elsewhere on the back. The
hairs in the vicinity are frequently matted, as if with a secretion. In
worn stage of pelage the gland may be visible from above without
separating the hairs. Bailey has suggested that this functions as an oil
gland for dressing the fur, and our observations bear out this view.
Kangaroo rats kept in captivity without earth or sand soon come to have
a bedraggled appearance, as if the pelage were moist. When supplied with
fine, dusty sand, they soon recover their normal sleek appearance.
Apparently the former condition is due to an excess of oil, the latter
to the absorption of the excess in a dust bath. The oil is doubtless an
important adjunct to the preservation of the skin and hair amid the
dusty surroundings in which the animal lives.