M A M M A L I A. 



Opposite side, and thus the two holds give firmness 

 to each other. The hind feet have five crooked claws 

 on each, and as they have in addition bent legs to 

 press them to their points of adhesion by the weight of 

 the body, they take a greater hold than the thumb 

 claws, proportional to the greater weight which they 

 have to sustain. 



In consequence of this disposition of the claws 

 when the animal is in a state of repose, very small 

 irregularities of surface will enable a large bat to 

 maintain its place with great firmness. Its position 

 too is a position of perfect repose, and not one main- 

 tained by muscular exertion, for the whole is done 

 by the elasticity of the tendons and ligaments. There 

 is yet another peculiarity in this position, especially 

 that of the hind legs, when the animal wishes to get 

 into motion, the unbending of the hind legs throws 

 the axis of the body upward, and opens the para- 

 chute, so that the air is under it, and the wings are 

 ready for acting in flight, the moment that the hooks 

 of the thumbs quit their hold. Getting to the wing 

 from the ground is a much more serious matter, and 

 we believe it may be said that, generally speaking, 

 bats crawl up some surface which is perpendicular, or 

 nearly so, when they take the wing. They are so 

 seldom seen on the ground, however, that it is impos- 

 sible to speak with perfect confidence about their 

 movements under all the variety of circumstances to 

 which they may be exposed, except by analogy from 

 their structure. 



On the ground, the action of the bat is peculiarly 

 awkward, more so than that of any other mammalia. 

 They cannot walk on all fours in the usual style, and 

 as little can they, from the singular way in which the 

 hind legs are articulated, and the weight of the fore 

 part of the body, raise themselves into an erect posi- 

 tion and walk upon these legs. The shoulder-joints 

 are articulated for motion across the axis of the body, 

 and therefore, independently of the awkward form of 

 the terminal portion of these extremities, the humerus 

 cannot be advanced so as to take any thing that can 

 be called a step : they are therefore reduced to a 

 very odd sort of motion ; they advance one side of 

 the body a little, which advances the bend of the 

 wing or elbow joint on that side, and having done so, 

 they lay hold in advance with the claw of the 

 thumb. This being done, they, by the unbending of 

 the hind leg, swing the body round upon this claw as 

 a pivot, by which operation, the turn of the wing on 

 the other side is brought in advance, and grappled by 

 means of the thumb claw in the same way as the 

 former. Repeating this operation with each side 

 alternately, they contrive to wriggle along by a course 

 something like that of a ship working board and board 

 upon a wind, and thus the resulting course is in a 

 straight line, though the actual motion is performed 

 alternately right and left. A motion which is so 

 laborious in the performance, and in which so little 

 progress is made, can be of comparatively small use 

 to the animals, as it can neither serve them in follow- 

 ing their prey, or in escapingTrom an enemy. They 

 therefore resort to it only in cases of necessity, and 

 if they have to practise it for any length of time, they 

 are completely exhausted. 



Bats are the only mammalia which can actaally 

 fly that is, which can renew their motion by gaining 

 a fresh impetus from the stroke of their flying mem- 

 branes against the air ; for all other animals which 

 have produced membranes which they can extend by 



stretching out their legs lateral^, use those mem- 

 branes only to prolong a spring which is originally 

 taken from some solid fulcrum of resistance. A con- 

 trivance of this kind would be of little or no use to a 

 ground animal, because the less resistance the air 

 offers to such an animal, the more rapidly it can 

 proceed, and also with the less effort of muscular 

 strength, consequently, those parachute membranes 

 as we may term them, are found only among climbing 

 animals, and among that description of them which 

 do not m;ike their progress by grasping, but by 

 running along the branches, and holding on with the 

 claws. Some of them, however, have a great deal of 

 freedom of motion ; and the common squirrel, the 

 membranes of which are very little produced, can 

 make its way very rapidly through the upper branches 

 of a clump of trees ; and even when it is alarmed, 

 it very rarely misses its footing or its hold, and falls 

 to the ground. The proper place to mention such 

 animals will be, however, that where we treat of 

 climbing organs, and the auxiliary organisations, by 

 means of which climbing animals contrive to pass 

 from branch to branch, or from tree to tree, when the 

 distance is too great for being reached by their limbs, 

 or cleared at an ordinary leap. 



Organs of Swimming. As the bodies of almost all 

 mammalia, when the lungs are inflated with air, are 

 of nearly the same specific gravity as water, they may 

 be said to be all capable of floating in that element ; 

 and as their so floating does not deprive them of 

 their powers of locomotion, they in general can row 

 themselves along by the action of their feet. This 

 is a sort of swimming ; but still with exceedingly few 

 exceptions, if indeed there are any, mammalia of this 

 description have the feet as well if not better adapted 

 for some khid of motion upon land than for this 

 description of swimming. When the water is to a 

 considerable extent the pasture or the element of 

 these mammalia, as in the case of the beaver and the 

 otter, the hind feet have the toes webbed ; and there 

 are some instances, such as that of the orriithorynchus, 

 where the webs of all the feet are very much pro- 

 duced'; but animals having this structure, live 

 habitually in the water, unless when they come up 

 to breathe, or when one pool dries up, and they have 

 to seek their way to another. The motions of none 

 of these, whether performed on the surface of the 

 water or under it, is the characteristic swimming 

 which distinguishes the proper vertebrated animals of 

 the waters, the fishes, from the other three classes. 

 The seals and narwhals have much more of the 

 swimming habit ; but still they are capable of some 

 motion on solid surfaces, for they can creep and they 

 can climb, they therefore retain in part that cha- 

 racter of the extremities which is perfect in laud 

 mammalia ; and in order rightly to understand the 

 typical organisation of mammalia for swimming, so as 

 to be able properly to compare it with the organi- 

 sation of the same general structure for the other 

 kinds of motion, we must turn to the cetacea. 



In the article CETACEA there will be found an 

 enumeration , of the principal species, and some 

 account of their structure and habits, so that all which 

 remains to be done in this place is, to take the most 

 typical one in illustration of the whole, and there is 

 none so well adapted for this purpose as the common 

 Greenland whale(/?rt/<TM mysticetus), which is unques- 

 tionably the best and the most constant swimmer of 

 the race. There is sufficient reason why this should 



