BAT 377 temporal bone containing the organ of hearing is much developed ; they all have canine and incisor teeth, the latter varying in number from 2 to 4 in the upper, and from 2 to 6 in the lower jaw ; the molars also vary from 3 to 6 in each jaw. The vertebrae of the neck are very broad ; those of the back and loins are simple and almost without spinous processes, and much compressed at the side ; the sacrum is very long and narrow ; the tail, when present, is short, and of use to support the interfemoral membrane and direct the flight. The number of vertebra) in pteropus is probably less than in any other mammal, being only 24. The ribs are remarkably long, as is the breast bone ; the upper part of the latter is greatly expanded laterally, to give a firm support to the very strong collar bones ; the front of the bone has also a crest, like the keel of the bird's sternum, and for a similar purpose, viz., the origin of the powerful muscles of flight. As the collar bone, so the shoulder blade is highly developed, es- pecially in the active insectivorous bats ; the arm bone is very long and slender ; the forearm consists of the usual two bones, but the ulna is quite rudimentary, and is united to the radi- us ; the latter is very long and robust, and can- not be rotated, an admirable provision for an animal whose progression requires a constant resistance to the air. But the most remarkable modification of the anterior extremity is in the hand ; the bones of all the fingers, except the thumb, are extremely elongated, for the at- tachment of the flying membrane ; the thumb is comparatively short, and provided with a hooked nail, by which the animal can climb or suspend itself. The thigh bone is of moderate size, and so turned that the front surface is directed nearly backward ; the fibula is quite small and slender, and has the remarkable con- dition of deficiency in its upper portion, the usual state of things being the reverse. The foot is not developed like the hand, the only peculiarity being a long-pointed btoy process arising from the heel, and enclosed in the mem- brane between the legs ; the toes are 5 in num- ber, nearly equal, and furnished with hooked nails, by which they suspend themselves when at rest, with the head downward. The seem- ing deformity and ugliness of the bats led the ancients to consider them as impure animals ; even ancient naturalists display the grossest ignorance concerning them. Aristotle, Pliny, and others, considered them as birds ; these opinions were copied during the middle ages, and are even now entertained by many per- sons. The faculty of flight depends on an entirely different organization in the bird and in the bat. The principal part of the bat's flying membrane is stretched between the enormously elongated fingers, and from them reflected to the posterior extremities ; but in the bird, the parts which correspond to fingers are so rudimentary that the hand can hardly be said to exist ; the wings extend beyond it, bearing the quills, the principal part, which belong to the epidermic system ; the wings in the two cases are in no respects homologous. The bat, so active in the air, is very awkward on the ground. When the animal attempts to walk, the wings are shut and become fore feet ; the hook of one thumb is fixed to some object, and by it the body is pulled forward and to one side, the next step being by a simi- lar movement by means of the hook of the other thumb. By this diagonal tumbling, the bats progress on a level surface ; the length of the wings prevents them from rising from such a situation, and it is only when they gain some trifling elevation that they can commence their flight. In the air they are perfectly free, and when desirous of rest they seek some dark re- treat, from the top of which they can hang, head downward, suspended by their hind claws ; in case of danger, they have only to loose their hold, when their wings are at once spread. The diminutive size of the eyes is well known, and familiarly expressed in the very common saying, " as blind as a bat." The insectivorous group, whose ears are largely developed, have very small eyes, placed almost within the auri- cle and concealed by the hair ; but in the fruit-eating genera the eye is of the usual size, as is also the ear. The diminutive eye is compensated for by the great development of the organ of hearing ; the external ear is enormously large, in the pleiotm auritus nearly Long-eared Bat (Pleiotus auritus). as long as the body ; there is a proportionate increase in the extent of the internal ear. The organ of smell in many insectivorous bats, as the rhinolopJiidce, is exceedingly acute ; it is provided with folds of the integument, of great size and the most grotesque forms, ren- dering their physiognomy like that which would be produced by a nose turned inside out and complicated by a hare-lip. These appendages are found in the groups whose habits lead them into the darkest caverns,
