The Lemurs comprised in the present Sub-family are divisible into two
groups--those inhabiting the mainland of Africa and those confined to the
island of Madagascar. The exclusively African species, the True Galagos,
constitute the single genus _Galago_; while the Malagasy group is
represented by three genera, the so-called Fat-tailed Lemurs (_Opolemur_),
the Dwarf-Lemurs (_Microcebus_), and the Mouse-Lemurs (_Chirogale_). The
members of this Sub-family vary considerably in size, and are all covered
with soft woolly fur. Their ears especially are largely developed, being
more or less membranaceous and naked, and their sense of hearing very
acute. The eyes are large and the tail always elongated. In the skull the
length of the muzzle is less that the greatest longitudinal diameter of the
orbit (except in the genus _Galago_). {38}Their teeth number 36--18 above
and 18 below--as in the bulk of the _Lemuridæ_; the upper molars present on
their crown an oblique ridge from the outer hind cusp to the inner front
cusp. The ankle region (_tarsus_) of the hind-limb is much elongated,
through the lengthening of two of its bones (the _calcaneum_ and
_naviculare_): this feature occurring to a greater extent among the African
than among the Malagasy species. The mammæ are four in number, two on the
breast and two on the abdomen.
Many of the species hibernate during the dry winter season, and to enable
them to survive, they accumulate during the summer months a thick deposit
of fat over their bodies, more especially at the root of the tail, a fact
first conspicuously observed in the Opolemurids. This fat is absorbed for
their sustenance during their prolonged torpidity.