Page:Encyclopædia Britannica, Ninth Edition, v. 15.djvu/428

Rh widely from all other mammals in external form, it is evident that this is but the result of special adaptation to aerial locomotion ; and, taking into account their whole bodily structure, we are forced to admit with Professor Huxley that they may be regarded as exceedingly modified Insectivora. So thoroughly, however, ha,s this adaptation been carried out that of all animals the Bats are the least terrestrial, not one of them being equally well fitted, as most Bird? and Insects are, for progression on the earth. This is due to the hind as well as the fore limbs being pressed into the service of aerial locomotion. The hind limb is so rotated outwards by the wing-membrane that, contrary to what obtains in all other vertebrates, the knee is directed backwards, and corresponds in position to its serial homologue the elbow. When placed on the ground, [cHIPvOPTERA. From the first thoracic to the last lumbar vertebra the spinal column forms a single curve backwards, which is most pronounced in the lumbar region. The bodies of the vertebrae are very slightly movable upon each other, and in old individuals appear to become partially ankylosed together. The caudal vertebrae are simple cylindrical bones without processes ; their number and length is extremely variable even in closely allied species ; and the anterior vertebrae are generally united to the ischial tuberosities. The development of these vertebrae, in fact, is intimately correlated to the habits of the animals, the long tail in the insectivorous species supporting and controlling the position of the large interfemoral membrane which appears not only to aid their rapid doubling motions when in pursuit of their insect prey by acting as a rudder on the air, but also to assist them in the capture and retention of the larger insects ; in the frugivorous species, on the other hand, this is not required, and the tail is accordingly rudimentary or absent. In all Bats the prestemum has a promi nent keel for the attachment of the great pectoral muscles. In most species the ribs are much flattened, and in some partially ankylosed by their contiguous margins. Great as is the variability of the shape of the skull in Insectivora, it is still greater in Chiroptera, and evidently depends upon the much wider differences in the nature of the food of different species requiring corresponding modifications of the man ducatory apparatus, so that extreme modi fications may be found in species of the same family, as in the case of the Phyl- lostomidx. In some genera, however, as in Miniopterus, Furia, Mormops (vide infra), the peculiar shape of the skull cannot thus be accounted for. As in the Insectivora, post-orbital processes are de veloped in some species only, as in the FIG. 65. Skeletonand Volar Membranes of the Noctule Bat (Vesperugonoctula). xi. c, clavicle; h, hum eras; ~PtamvmK,l a&amp;gt; onrl in o fnw Niirtevirliv an/1 r, radius ;, ulna (rudimentary) ; d first digit or pollex ; d~, d*, d*, d*, other digits of the manus sup- J rOpOWia dim 111 d lew M ytiei W porting um, the wing-membrane ; m, m, metaearpal bones ; p/i l , first phalanx ; ph 2 , second phalanx ; ph 3 , Emballonuridse , in PteropUS leucopterilS third phalanx; am, antebrachial membrane;/, femur; /, tibia ;/6, fibula (rudimentary) ; c.calcaneum i i nrnpp&amp;lt;5&amp;lt;5 from flip 7vorvmaHp or calcar supporting im, the interfemoral membrane ; pel, post-calcaneal lobe. P lul ^t!bb u nits yguiud,i/ii arch meet the post-orbital so as to corn- therefore, the animal rests on all fours, having the knees directed upwards like a grasshopper s, while, in order to bring the foot into a position for forward progression, it is rotated forwards and inwards on the ankle. Walking under these circumstances is at best only a species of shuffle, and that this is fully recognized by the animal is evidenced by its great anxiety to take to the wing, or, if this be impracticable, to ascend to soms point where it can hitch itself up by the claws of the hind-legs in its usual position when at rest. The bones entering into the formation of the skeleton in Chiroptera are characterized by their slendemess, and by the great size of the medullary canals in those of the extremities. The vertebral column is short, and the vertebrae differ very slightly in number and form through out the species. The general number of the dorso-lumbar vertebras is 17, whereof 12 are dorsal; the cervical vertebrae are very broad, but short from before backwards (their breadth is due to the great transverse diameter of the spinal canal rendered necessary by the comparatively very large siza of the spinal cord in this position, which, after giving off the nervous supply to the fore limbs and thorax, rapidly diminishes in size, and in the lumbo-sacral region is reduced to a fine thread). Except in the great frugivorous Bats (Pteropodidae), the vertebrae, from the third cervical backwards, are devoid of spinous processes, a characteristic feature in the general osteology of the order. plete the orbital ring. Zygomatic arches, though slender, are present in all except in some of the species of Phyl- lostomidx, The milk teeth differ from those of all other mammals in that they in no respect resemble in form those of the permanent series. They are very slender, with acutely pointed recurved cusps, and are soon shed, but often coexist for a short time with the permanent teeth when the latter are considerably elevated above the gum. In the family Mhinolophidas the milk teeth are absorbed before birth. The permanent teeth exhibit great variety in form, sometimes even in the same family, as in Phyllostomidse, whilst in other families, as in Rhinolophidx, the resemblance between the dentition of species otherwise differing in many important respects is most remarkable. In all, however, they are provided with well-developed roots, and their crowns are acutely tuberculate, with more or less well-defined W-shaped cusps, in the insecti vorous species, as in Insectivora, or variously hollowed out or longitudinally grooved in the frugivorous, as in some species of Phyllostomidss and in the Pteropodidse. As might be expected, the shoulder-girdle varies very slightly, having the same office to fulfil in all species. The clavicle is very long, strong, and curved ; the scapulae large, oval, triangular, with a long curved coracoid process. The humerus, though long, is scarcely two-thirds the length of the radius ; the ulna is rudimentary; its proximal extremity,