STRUCTURE. The vertebral column is short and compact, the thorax capacious, to make room for the proportionately very large heart and lungs, and the breast-bone (which is keeled like that of birds) and shoulder-girdle are very large and strong to afford attachment to the great muscles operating the wings; while the pelvic girdle is small and weak. Reversing the rule among mammals, the fore-limbs are developed vastly in excess of the hind ones, which, although provided with perfectly formed feet, are practically useless for locomotion on the ground. though of service in climbing. and particularly in clinging to some support, from which the creature hangs head down when at rest—its customary attitude of repose. The bones of the limbs are permeated by medullary canals so large as to make them prac tically hollow; other bones are light and slender, and the ribs much flattened.
Wings.—The modifications of the limbs with reference to flight are very great (see illustra tion). The shoulder-bones (clavicle and scapula).
are much enlarged and strengthened. The hu merus (h), though long, is scarcely two-thirds as long as the forearm, where the radius (ur) is so lengthened that in some species it is as long as the head and body together (the ulna is rudi mentary and firmly soldered to the radius) ; the wrist or carpal bones (c) are compact, and more or less soldered together at the radial joint; the metacarpals (m, equivalents of the bones of the 'back' of the human hand) are prolonged to lengths varying in the different families, but always equaling or exceeding the length of the body. and terminate in fingers (d) consisting of a varying number of phalanges. An exception to this, however, is made by the thumb (t), which is very short, free from the wing-membrane, and terminated by a strong claw greatly used by the animal in climbing or hold ing on to a support. Thus the length of the arm and hand may be 15 or 20 times as great as the breadth of the shoulder.
The position of the bones is changed, so that while ability for a rotatory motion is lost, greater power for an up-and-down (antero-pos terior) motion is gained. The hind-limbs are also lengthened in the leg-bones; but here the notable change is in the lateral position and spread gained through a twisting outward so extensive that the knee is directed backward in stead of forward. Upon this light, strong frame work, moved and controlled by powerful pectoral muscles, is stretched a flexible, leathery, nearly hairless membrane (patagium). which is double, and is really an extension of the skin. It en velops all the bones of the arm and hand, and thence stretches to the bind-leg (leaving the foot free), and in most families to. or nearly to, the end of the tail; but its relative size and shape vary. Stretching this great membrane and beating the air with it. the hat flies with more than the agility of a bird, though more slowly, and when it rests it folds the membrane somewhat like a fan against its sides, or wraps it about its body like a protecting mantle.
SceRe-Orgons.—The brain and nervous system of bats are comparatively low in organization. hut their sensory faculties are remarkably developed in adaptation to their crepuscular and nocturnal habits. As blind as a bat,' is a mistaken simile. All have efficient eyes, those of the Oriental fruit-eating sorts being of a size natural to their fox-like countenances. In our more familiar insect-eating species they are likely to he small, head-like, and nearly hidden in the very soft fur with which these animals are clothed: the old English and German names 'flitting mice,' were not bad ones. The senses of smell and taste are probably well developed. The sense of hearing is no doubt exceedingly acute and largely de pended upon. All bats have prominent and very mobile ears, and in many of the insect-eaters, the external ear expands in an enormous membrane, sometimes many times larger than the whole face, supplemented by appendages. ribbed, crinkled, and otherwise modified, and in some forms able to be folded down out of the way of harm. These expansive ears are evidently of more utility than simply to catch waves of sound. and are related to the extraordinary sense of touch, which perhaps is carried to a higher de gree of delicacy in these than in any other ani mals. In addition to them a large section of the order possesses 'nose-leaves'—mo•e or less wrinkled and complicated upright growths of thin skin from the end of the nose, which often give to the face a most grotesque appearance. Two of the most extraordinary examples are shown on the accompanying plate — the flower nosed bat (Fig. 7). a native of the Solomon islands: and Blainville's chin-leafed bat (Fig. 5) of South America. On the other hand, in some species such appendages are wholly absent, as in the ugly naked hat (Fig. 3) of the Malay coun tries.
All these membranes, as well as those of the wings. are filled with blood-vessels and numerous ramifications of fine nerves. which take the form elsewhere seen in especially sensitive surfaces, and they are regarded as apprising the creature, in a way not fully understood, of the nearness of obstacles, and giving other useful information. This was illustrated by the celebrated experi ments of Spallanzani, about 1775. He blinded bats with varnish, and let them fly in a chamber filled with stretched and dangling strings. These and other obstacles they avoided: they turned corners. found holes for escape or concealment, and behaved as though eyesight were unneces sary; stoppage of the ears, however, caused them some embarrassment. Other observations have confirmed their ability, apparently through ex treme sensitiveness of the exposed membranes, to -sense objects without sight or actual touch.