BATS. 



SIS 



of a bat through the air the flight of a bird. The 

 ostrich balances a horizontal spine upon two legs, 

 and a large portion of the middle of that spine is so 

 inflexible, that it may be considered as a sort of beam 

 or balance, poised on the articulations of the sup- 

 porting legs. But the articulations of the vertebrae 

 of the mammalia all (with the exception of some in 

 the necks only of a few species), admit of motion ; 

 and, therefore, there is no part of their spine which 

 can be balanced like a beam, upon two legs articu- 

 lated a.t the same distance from the extremities. 

 Consequently, they cannot stand or walk upon two 

 legs but with the spine in an erect posture, so that 

 each vertebra may support the portion above it. 



The back bone of a bird, from the insertion of the 

 neck to that of the tail, may therefore be considered 

 as an inflexible beam or lever (at least it is nearly so), 

 supported upon the articulations of the legs as a 

 fulcrum, and, by the well known property of the 

 balance, capable of being held in equilibrio at any 

 angle, except perpendicularly to the horizon, the 

 flexible neck and tail, and the bondings of the joints 

 of the legs, being the means by which it is kept in 

 equilibrio. In as far as support is concerned, it is 

 evident that if any body is supported on a point, 

 that point may be moved, and the supported body 

 along with it, in any direction and with any velocity, 

 without in the least disturbing the equilibrium of the 

 body. The point upon which the body of a bird is 

 supported, is always in the line joining the articula- 

 tions of the legs, in the middle where the bird stands 

 equally on both feet, and nearer the supporting foot 

 when it stands unequally ; and the motions of the 

 head and tail enable the bird to swing upon this 

 point, without the least tendency to fall. If the 

 bird had any other supports, these would prevent the 

 motions of its body, and actually render it unstable. 

 So that the two feet of the bird perfect its support in 

 standing or walking on the ground ; and when the 

 habit of the bird is also to fly (which is the general 

 one), its wings are left entirely free, or available for 

 aerial purposes. When the bird flies, the point of 

 support is transferred to the line of the wings, on 

 which the balance is as complete and independent as 

 that on the feet. The bird has thus two systems 

 of motive organs, feet for the ground and wings for 

 the air ; and each of these is perfect in itself, and 

 independent of the other. We shall show that the 

 mammalia can have only one system ; and, therefore, 

 must be either walkers incapable of flight, as in the 

 majority, or flyers incapable of walking, as in the bats. 

 These are no doubt balancing wings, and partially 

 also swimming wings, the structure and action of 

 which will be explained in the article BIRD ; but it 

 is not necessary to allude to them here, as they form 

 no part of the structural distinction between a bird 

 and a bat. 



But if the spine of a bird resemble a beam or 

 lever, which can be supported and balanced on one 

 point, that of the mammalia resembles a chain, which 

 unless it can be supported on end, as in the case 

 with man, must have two points of support. A chain 

 can merely hang across one support placed not at its 

 extremity ; and a certain degree of tension is requi- 

 site for keeping it in any form upon two, as, left to 

 its gravitation, it would fall into the well known curve 

 called the catenary (or chain curve). The system of 

 muscles with which the spine of the mammalia is 

 furnished gives this tension, and the spinous processes 



of the vertebrae, which have often so singular an 

 appearance, are the levers upon which these muscles 

 act in putting the spine into the position required. 

 But still no action of muscles on the flexible spine 

 could keep that supported upon a single point, unless 

 nearly on end, as in man. 



Therefore, it is not possible to give to the mam- 

 malia two sets of motive organs, one for walking and 

 one for flying, as in birds ; because both sets of extre- 

 mities are necessary for supporting the body both on 

 the ground and in the air. In all reasonings on 

 the comparative structures of animals, man must be 

 left out ; because none other of the mammalia have 

 only two walking feet, and none two hands of all 

 work. Apes cannot walk long in the erect posture, 

 and they walk awkwardly, while all the other mam- 

 malia, unless they use all their four feet in walking, 

 merely shuffle along in a sort of sitting posture ; and 

 if they were to attempt to walk fairly balanced on 

 their hind legs, the fore part of the body would fall 

 down. So also, though they had wings in place ot 

 the fore legs, they could not use these wings fol 

 flying. They might assist in a leap, like a parachute ; 

 but the moment that the body were committed to 

 them, the hinder part would fall down, in conse- 

 quence of the flexibility of the spine ; the body would 

 turn on the axis of the wings till these were on edge ; 

 arid then it would tumble to the ground with the 

 head or the heels foremost, according as the one or 

 the other weighed heavier from the axis of the wings. 

 If the spine were inflexible, so that they could balance 

 themselves on wings, they could not use four feet in 

 motion, or turn round without much labour. Some 

 of the saurian reptiles turn with much difficulty, on 

 account of their stiff scaly coverings, though they 

 have articulated spines. 



Thus much of the general principles of animal 

 mechanics is absolutely necessary, in order to have 

 any thing like clear notions of the structure and 

 motions of bats ; for as all animals are made of 

 matter, and subject to the laws of matter, no animal 

 can act in opposition to those laws without an appa- 

 ratus capable of overcoming them. A foot cannot 

 walk, or a wing fly, unless it accord with the general 

 organisation of the body ; and two structures which 

 are incompatible with each other cannot act at all. 

 The winged horses, and the winged beings otherwise 

 in human shape, which we meet with in paintings and 

 sculptures are, on this account, incongruous combina- 

 tions ; and if the beings which they are meant to 

 represent could not fly without the wings, they could 

 not possibly fly by means of them, as the action of 

 wings is perfectly incompatible with that of fore legs 

 or arms. 



It was similar ignorance of, or want of attention 

 to, mechanical possibility and consistency, which led 

 to the confounding of bats with birds ; but as 

 the principles of zoology began to be better under- 

 stood, and animals were classed more according to 

 their physiology, it was admitted that the bats were 

 true mammalia; and in consequence of the pectoral 

 mammaj of the females, and some other external 

 appearances, Linna-us placed them in the same order 

 with man and the ape tribe. 



The faultiness of that classification is easily seen ; 

 but it would seem much more easily seen than cor- 

 rected. Cuvier ranks them and the other cheiroptera 

 as the first family of his great order Carnassicrs, of 

 which the Carnivora form another family. This is 



