MAMMALIA. 



133 



classes, as a few of both live upon vegetables, though 

 by far the greater number are animal feeders. Con- 

 sidering: these circumstances, we shall notice their 

 organs of motion separately from the rest, inasmuch, 

 as all the other mammalia make the successive steps 

 of their advances from solid supports, whether the 

 length of the step be longer or snorter, and whether 

 it be or be not prolonged by membranes which, like 

 parachutes, take hold in the air, and prevent them 

 from having so much downward motion as the natural 

 gravitation of the mass of their bodies wouldgive them. 

 Organs of flying. We shall, in our summary of the 

 systematic arrangement of mammalia, mention the 

 characters of the different groups which make up the 

 numerous and widely distributed family of cl/ciro- 

 pterous, or volant mammalia ; and therefore, as our 

 object in the mean time is to point out those devia- 

 tions from the typical structure, as already described 

 in that of the human body, we shall confine our ob- 

 servations to the bats, which are by far the most 

 characteristic, and the ones which are most efficient 

 in aerial motion, and least so in progressive motion 

 along the ground. Indeed they are less effective 

 upon the ground than any of the air birds, the swifts 

 hardly excepted, which are rarely seen but on the 

 wing, or clinging to the sides of high rocks and lofty 

 towers in the same manner, though not by exactly 

 the same kind of organisation, as the bats cling to 

 the internal surface of caves, the undersides of the 

 branches of shadowy trees, and other objects by which, 

 as they are nocturnal animals, they may be protected 

 from the direct light and heat of the sun, which no 

 nocturnal animal can well endure. It will facilitate 

 our explanation more if we introduce the skeleton of 

 a bat. than if we were to give figures in detail of 

 those parts which contribute to the peculiar action of 

 these animals ; because, as the form and articulations 

 of the skeleton determine the general motions, it is 

 not difficult for the imagination of any reader who is 

 tolerably acquainted with the organisation of any one 

 of the mammalia to understand any other as clothed 

 with soft parts, answering to the peculiarities of the 

 skeleton. The figure represents the skeleton of a bat. 



The parts of the skeleton here, that is, the grand 

 divisions of head, trunk, and members, are the same 

 in number and general position with regard to each 

 other as they are in man ; but they differ greatly in 

 their form, the development of their different parts 



and in the details of the extremities. On examining 

 the anterior extremities, which we shall call the 

 wings, though in every respect they differ from the 

 wings of birds, it will be found that they differ greatly 

 from those of mammalia, which have "not the power 

 of flight, whether the principal action of the fore 

 extremities in these be progressive motion or any 

 thing else. It will be seen that the scapula or blade- 

 bone is very large, which affords it a firm embedment 

 among the muscles on the back, and that the clavicle 

 which forms the reacting bone, and keeps asunder 

 the two sockets which receive the heads of the 

 humeri or arm bones is also very strong for the 

 general mass of the skeleton. The coracoid bone, as 

 already noticed, is wanting, however, and the clavicles 

 extend directly to the sternum and bear upon it, 

 instead of forming a distinct arch or furcal bone, as in 

 bird?. The support of the shoulder joint is thus very 

 strong for the size and strength of the animal ; but it 

 has not the same steadiness as the shoulder joint of a 

 bird, which rests upon a tripod, and as the middle 

 bone of that tripod, the coracoid, abuts firmly on 

 the sternum, while the others are com paratively" free, 

 the one in its arch, consisting of the two lateral por- 

 tions united, and the other in its embedment entirely 

 among flesh ; the sternum is the bone upon which a 

 bird is really carried when supported by the action of 

 its wings in the air. In the bat, on the other hand, 

 the shoulder joint is supported by only two bones, 

 and therefore the bearing up of the body in flight is 

 thrown as much, if not more, upon the muscular 

 attachment of the blade-bone to the ribs as upon the 

 sternum. The bat is thus supported in its flight in 

 the same manner as other mammalia are supported 

 in their motions, in which the feet are the points 

 from which the motion is taken, and the origin of it 

 is from solid substances ; and the remarkable part of 

 this structure in the bat is such a modification as 

 enables it to originate motion by striking its extre- 

 mities against the air. To produce this modification, 

 there must be powerful muscles to depress the wings 

 in taking the stroke ; and in order that those muscles 

 may act with proper effect, they must have a place 

 of origin proportionally firm to that of the joints of 

 the bones to which they are attached. For this pur- 

 pose the sternum is provided with an elevated keel 

 along the mesial part, and to this keel the principal 

 muscles which depress the wings are attached. 



The bones of the fore-arm, and more especially 

 those of the metacarpus and the phalanges of the 

 fingers, or as we may call them, the four external 

 toes, in each of the fore extremities, are very long and 

 slender in proportion to their length, so that this 

 part of the skeleton is slender and light to its ex- 

 tremity ; and these terminal bones spread very wide 

 at their extreme points. The thumb or inner toe on 

 these extremities is comparatively short, and it is 

 furnished with a strong and very crooked claw which 

 assists the animal in suspending itself from the rug- 

 ged surfaces to which it clings, and also in its slow 

 and crawling motion upon the ground. From the 

 nature of the shoulder joint in wanting the third 

 means of support ; from the length and slendciness 

 of the bones, and the distance to which they are 

 spread from each other at their extremities, and from 

 the immediate organ of flight being membrane sup- 

 ported by bone and not feathers, this wing is much 

 less efficient in proportion to its size than the fea- 

 thered wing of a bird, and it is incapable of that 



