species bats membrane bones short size developed position bone body
MAMMALIA ORDER CHIROPTERA, volant mammals, having their fore limbs specially modified for flight. The forearm consists of a rudimentary ulna, a long curved radius, and a carpus of six bones supporting a thumb and four greatly elongated fingers, between which, the sides of the body, and the hinder extremities a thin expansion of the integument (the wing- membrane) is spread out. The knee is directed backwards, owing to the rotation of the hind limb outwards by the wing-membrane ; a peculiar elongated cartilaginous process (the calcaneum or calcar), rarely rudimentary or absent, arising from the inner side of the ankle-joint, is directed inwards, and supports part of the posterior margin of an accessory membrane of flight, extending from the tail or posterior extremity of the body to the hinder limbs (the inter-femoral membrane). The penis is pendent • the testes abdominal or inguinal ; the mammary glands thoracic and generally post-axillary ; the uterus simple er with more or less long cornua ; the placenta discoidal and deciduate ; and the smooth cerebral hemispheres do not extend backwards over the cerebellum. The dental series consists of four kinds of teeth - incisors, canines, premolars, and molars ; and the dental formula never exceeds i 4, c 4, pm, 3i m 4 ; total 38 teeth.
The animals comprised in this order are at once distinguished by the presence of true wings, and this peculiarity is accompanied by other modifications of bodily structure having special relation to aerial locomotion. Thus, in direct contrast to all other m immals, in which locomotion is chiefly effected by action from behind, and the hind limbs consequently greatly preponderate in size over the fore, in the Chiroptera the fore limbs, being the only agents in propelling the body forward during flight, immensely exceed the short and weak hinder extremities ; the thorax, giving origin to the great muscles which sustain flight, and containing the proportionately (compared with other mammals) very large lungs and heart, is remarkably capacious, and the ribs are flattened and close together ; the shoulder-girdle is also greatly developed in comparison with the weak pelvic bones.
Limmus included the Bats among the Primates, mainly on account of the number of their upper incisors, supposed to be always four, the thoracic position of the mamma;, and the pendent condition of the penis. Many other zoologists, taking into consideration also the placental characters and the form of the uterus, have followed him ; but it is evident that the situation of the mammm is related to the necessarily central position of the young during flight, the shortness of the uterine cornua, observable in so many species, to the generally uniparous gestation requiring less room, while the discoid deciduate placenta is equally present in and characteristic of the Insectivora, many species of which have also the penis pendent. Then, all these reasons for maintaining the Bats in such an exalted position being disposed of, we find in the low organization of their brain another proof of their inferior position in the zoological scale, while furthermore, although they differ 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, has this adaptation been carriel out that of all animals the Bats are the least terrestrial, not one of them being equally well fitted, as most Birds 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, 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 some 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 Chitoptera are characterized by their slenderness, and by the great size of the medullary canals in those of the extremities. The vertebral column is short, and the vertebra differ very slightly in number and form throughout the species. The general number of the dorso-lumbar vertebra is 17, whereof 12 are dorsal; the cervical vertebmve 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 size 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 (Pteropodida), the vertebra', from the third cervical backwards, are devoid of spinous processes, a characteristic feature in the general osteology of the order.
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 vertebrm are very slightly movable upon each other, and in old individuals appear to become partially ankylosed together. The caudal vertebrm are simple cylindrical bones without processes ; their number and length is extremely variable even in closely allied species ; and the anterior vertebra 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 presternum has a prominent 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.
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 Rhinoloplaida3 the milk teeth are absorbed before birth. The permanent teeth exhibit great variety in form, sometimes even in the same family, as in Phyllostomidee, whilst in other families, as in R.kinotophicim, 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 insectivorous species, as in Insectivora, or variously hollowed out or longitudinally grooved in the frugivorous, as in some species of Phyllostomidw and in the I'teropodithe.
As might he expected, the shoulder-girdle varies very slightly, having the same office to fulfil in all species. The clavicle is ver;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, which articulates with but a small part of the humerus, is ankylosed with the radius ; immediately beyond the joint it is reduced to a very slender splint-like bone, which extends about as far as the middle of the radius. In all species a detached sesamoid bone exists in the tendon of the triceps muscle, and is generally found in skeletons. The radius is very long, in some species as long as the head and body. The proximal row of the carpus consists of a single bone (the united scaphoid, lunar, and cuneiform bones), which, with the extremity of the radius, forms the radio-carpal joint ; in the distal row the trapezium, trapezoid, and os magnum vary much in size in the different families ; the unciform appears to be the most constant, and the pisiform is generally very small. It will be necessary to again refer to this subject when dealing with the diagnostic characters of the suborders.
The menus is, in all the species, composed of five digits. The first, fourth, and fifth consist each of a metacarpal bone and two osseous phalanges ; in the second and third the number of phalanges is different in certain families. The first digit - the pollex - always terminates in a claw, which, with the proximal phalanx, is most developed in the frugivorous species. In most of the species of the frugivorous Pteropodidw the second digit is also provided with a claw, but in all other Bats this and the remaining digits are unarmed. In the genus Triamops alone a very peculiar short bony process projects from the outer side of the proximal extremity of the terminal phalanx of the fourth digit. The relative development of the digits and their phalanges will be specially treated of under each family.
As might be expected from the small size of the posterior limbs, the pelvic girdle is very weak. The iliac bones are long and narrow. In most species the pubic bones of opposite sides are very loosely united in front in males ; in females they are widely separated ; in the family Phinolophid alone do these bones form a symphysis. The eminentia ileoTectinea develops in all species a long pectineal process, which in the subfamily Phyllorhininx alone is continued forwards to the anterior extremity of the ilium (vide infra, p. 412), forming a preacetabular foramen which is unique among mammals. The acetabulum is small and directed outwards, and slightly upwards, and with this is related the peculiar position of the hind limb described above as one of the chief characteristics of the order. The femur is slender and cylindrical, with a small head and very short neck, and scarcely differs in form throughout the species. The bones of the leg and foot are more variable ; in the subfamily ilio/ossinm alone is there a well-developed fibula ; in all other species this bone is either very slender or cartilaginous and ligamentous in its upper third, or reduced to a small bony process above the heel, as in Heyaderma, or altogether absent, as in .11Tycteris.
The foot consists of a very short tarsus, and of slender, laterally compressed toes, with much curved claws. The first digit is composed of a metacarpal bone, a proximal and an ungual phalanx, and is slightly shorter than the other four toes, which have each an additional phalanx, except in the subfamily Phyllorhininte and in the anomalous genera Tleyroptera and ifyxopoda, where all the toes have the same number of phalanges as the first digit, and are equal to it in length. In the very remarkable genus Cheiromeles the first digit is thumb-like and separated from the others ; and in the Holossi the first and fifth digits are much thicker than the intermediate toes.
The muscular system, as might be expected, exhibits few striking differences throughout the species. The most noticeable peculiarities in the myology of the order consist in the separated bands or slips into which the platysma is divided, and in the remarkable muscle termed occipitopollicalis, which extends from the occipital bone to the base of the terminal phalanx of the pollex (see Macalister, " Myology of the Chiroptera," Phil. Trans. _Roy. Soc., 1 S72).
Although, as above mentioned, the brain presents a low type of organization, yet probably no animals possess so delicate sense of touch as the Chiroptera. It is undoubtedly this perceptive power which enabled the individuals deprived of sight, hearing, and smell, in Spallauzani's well-known experiments, to avoid the numerous threads hung across the rooms in which they were permitted to fly about_ In the common Bats the tactile organs evidently exist, not only in the delicate vibrissm which spring from the sides of the muzzle, but also in the highly sensitive and widely extended integumentary structures entering into the formation of the wing-membranes and ear-conchs, while in many other species, notably in the tropical Rhinolophine and Phyllostomine Bats, peculiar foliaceous cutaneous expan- sions surrounding the nasal apertures or extending backwards behind them are superadded (vide infra). These structures, collectively known as the " nose-leaf " (whence the term " leaf-nosed Bats "), have been shown by the present writer (who has traced their gradual development in different species) to be. made up partly cf the extended and thickened marginal integument of the nostrils, and partly of the highly differentiated glandular eminences occupying the sides of the muzzle, in which, in all the common Bats, the vibrissae are implanted.
In all species of leaf-nosed Bats, and especially in th? R.hirro/ophidw, in which the nasal appendages reach their highest development, the superior maxillary division of the fifth nerve is of. remarkably large calibre. The nasal branch of this nerve, which is given off immediately beyond the infra-orbital foramen, is by far the largest portion, the palpebral and labial branches consisting of a few slender nerve fibres only. This branch passes forwards and upwards on the sides of the superior maxillary bone, but soon spreads out into numerous filaments which pass into the muscles and integument above, and into the base of the nose-leaf. The nerve supply of the nose-leaf is further considerably augmented by the large nasal branch of the ophthalmic division of the fifth nerve.
While the many foliations, elevations, and depressions which vary the form of the nose-leaf also greatly increase the sensory surface so abundantly supplied by the fifth nerve, and in rapid flight intensify the vibrations conveyed to it, the great number of sweat and oil glands which enter into its structure perform an important function, analogous to that of the glands of the auditory canal in relation to the membrane tympani, in maintaining its surface in a highly sensitive condition.
The nasal appendages of Chiroptera, then, may be regarded as performing the office of an organ of a very-exalted sense of touch standing in the same relation to the nasal branches of the sensory divisions of the fifth nerve as the aural apparatus to the auditory nerve ; for, as the latter organ collects and transmits the waves of sound, so the former receives impressions arising from vibrations communicated to the air by approaching objects.
In no order of mammals is the ear-conch so greatly developed or so variable in form ; in most of the insectivorous species the ears are longer than the head, while in some, as in the common Long-eared Bat (Plecotus auritus), their length nearly equals that of the head and body. The form of the conch is very characteristic in each of the families ; in most the tragus is remarkably large, in some extending nearly to the outer margin of the conch ; its office appears to be to cause undulations in the waves of sound, and so intensify and prolong them. It is worthy of notice that in the only family of insectivorous Bats wanting the tragus, the Bkino/opkidx, the auditory bulla osseze reach their greatest size, and the highly sensitive nasal appendages their highest development ; also in the group ilro/ossi the ear-conch is divided by a prominent keel; and the antitragus is remarkably large in those species in which the tragfis is minute (see fig. 66, a). In the frugivorous Bats, as might be expected, the form of the car-conch is very simple, and but slightly variable throughout the species.
In all Bats the ears are extremely mobile, each moving independently at the will of the animal. This has been observed by the writer even in the frugivorous Pteropodidx, in which the peculiar vibratory movements noticed by Mr Osburn in Artibeus perspicillatus may also be seen when the animals are alarmed.
The opening of the mouth is anterior in most species, hut in many it is inferior, the extremity of the nose being more or less produced beyond the lower lip, so much so indeed in the small South-American species Rynchonycteris naso as to resemble that of the Shrews. The lips exhibit the greatest variety in form, which will be specially referred to under each family. The absence of a fringe of hairs is very characteristic of all fruit-eating Bats, and probably always distinguishes them from the insectivorous species, which they may resemble in the form of their teeth and in other respects.
The oesophagus is narrow in all species, and especially so in the sanguivorous Desmodontes. The stomach presents two principal types of structure, which correspond respectively to the two great divisions of the order, the Megachiroptera and the Microchiroptera ; in the former (with the exception of Ilarpyia) the pyloric extremity is more or less elongated and folded upon itself, in the latter it is simple, as in Insectivora vera ; a third exceptional type is met with in the sanguivorous Desmodontes, where the left or cardiac extremity is greatly elongated, forming a lang narrow ccum-like appendage. The intestine is comparatively short, varying from one and a half to four times the length of the head and body, being longest in the frugivorous, shortest in the insectivorous species. In Rhinoponta nticrophyllum and .11egadernza spasma only has a very small cmcum been found. .
The liver is characterized by the great size of the left lateral lobe; which occasionally equals half the size of the whole organ ; the right and left lateral fissures are usually very deep ; in .32regctchiroptera (Ilarpyia excepted) the Spigelian lobe is ill-defined or absent, and the caudate is generally very large, but in Microchiroptera, on the other hand, the Spigelian lobe is very large, while the caudate is small, in most species forming a ridge only. The gallbladder is generally well developed and attached to the right central lobe, except in Rhinolophithe, where it is connected with the left central.
In most species the hyoid hones are simple, consisting of a chain of slender, elongated, cylindrical bones connecting the small basi-hyoid with the cranium, while the pharynx is short, the larynx shallow with feebly developed vocal cords, awl guarded by a short acutely-pointed epiglottis, which in some genera (Ilarpyia, ITampyrns, c.y.) is almost obsolete. In the Epomophori, however, we find a remarkable depart are from the general type: the pharynx is long and very capatious, the aperture of the larynx far removed from the fauces, and, opposite to it, a canal, leading from the narial chambers, and extending along the back of the pharynx, opens ; the laryngeal cavity is spacious and its walls are ossified ; the hyoid bone is quite unconnected, except by muscle, with the cranium ; the cerato-hyals and epi-hyals are cartilaginous and greatly expanded, entering into the formation of the walls of the pharynx, and, in the males of three species at least, supporting the orifices of a large pair of air-sacs communicating with the pharynx (see fig. 67).
In extent, peculiar modifications, and sensitiveness, the cutaneous system reaches its highest development in this order. As a sensory organ its chief modifications in connexion with the external ear, and with the nasal and labial appendages, have been described when referring to the nervous system. It remains therefore to consider its relative development as part cf the organs of flight.
The extent and shape of the volar membranes depend mainly on the form of the bones of the anterior extremities, and on the presence or absence of the tail. Certain modifications of these membranes, however, are met with, which evidently .do not depend on 'the skeleton, but are related to the habits of the animals, and to the manner in which the wing is folded in repose.
The velar membranes consist of - (1) the "antebrachial membrane," which extends from the point of the shoulder along the humerus and more or less of the forearm to the base of the thumb, the metacarpal bone of which is partially or wholly included in it ; (2) the " wing-membrane," which is spread out between the greatly elongatvl fingers, and extends along the sides of the body to the posterior extremities, generally reaching to the feet ; and (8) the " interfemoral membrane," the most variable of all, which is supported between the extremity of the body, the legs, and the calcanea (see fig. 65).
The antebrachial and wing membranes are most developed in those species which are fitted only for aerial locomotion, and which when at rest hang with the body enveloped in the wings ; but in the family Emballonuricla,,. especially in the subfamily Molossinie (the species of which are, of all Bats, the best fitted for terrestrial progression), the antebrachial membrane is reduced to the smallest size, and is not developed along the forearm, leaving also the thumb quite free, and the wing-membrane is very narrow and folded in repose completely under the forearm. The relative development of the interfemoral membrane has been referred to above in describing the caudal vertebrae.
ous glands and pouches opening on the surface • of the outer skin are developed in many species, but in most cases more so in males than in females, and so constitute very remarkpp. 241-252.) Space does not admit of entering here upon a special of in the works noted in the bibliography of the order below, and therefore with the above short account of the general structure of the species we proceed to cDnsider their classification and geographical distribution.
The Chiroptera fall naturally into two subdivisions, which may be called suborders.
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