Page:Natural History (1848).djvu/47

Rh Bats constitute an Order of Mammiferous animals so distinctly marked as to be recognised, without possibility of error, at a glance. The structure which belongs to them in common with other quadrupeds, is so modified as to give them the powers and habits of birds. This is effected by the elongation, to an extraordinary extent, of the anterior extremities, and particularly of the fingers, which, diverging from the wrist, afford so many spokes for the expansion of an attached membrane, as the ribs of an umbrella expand the silk. An extremely delicate and sensitive skin, copiously supplied with blood-vessels and nerves of sensation, commences at the sides of the neck, embraces the whole arm and hand, with the exception of the thumb, extends from the little finger to the instep of the hind foot, and thence to the tip or middle of the tail, where this organ is present, or, where it is absent, to the hinder part of the trunk. A lengthened bone, proceeding from the heel, assists the tail in the expansion of this interfemoral portion of the membrane, or where there is no tail performs that office alone, and gives to this part the power of governing the direction of the flight, like the spread tail of a bird.

The broad expanse of surface thus obtained is not merely available to sustain the animal upon the air, as by a parachute, in long leaps; but is