513 



LOCOMOTION OF ANIMALS. 



LOCOMOTION OF ANIMALS. 



514 



perfect the organ as an instrument of prehension, and adapts it for 

 climbing trees. Thus we find these animals are endowed with four 

 hands ; and hence their generic name of Quadrumana. The limbs, 

 being thus organised, may be used either as those of bipeds or of : 

 quadrupeds during progression. When the legs only are employed in | 

 locomotion on the ground, they obey many of the same laws as those , 

 of man, and the reader is referred to the account given of them in the 

 preceding part of this article for the general principles ; but the 

 mechanical structure of the chimpanzee and orang-outan renders their 

 gait peculiar, and their power of progression on two legs is inferior to 

 that of man. We observe amongst the higher orders of Quadrumana 

 that in walking the long arm of the orang is frequently placed on the 

 ground to prevent the trunk and head of these animals from falling 

 forwards. This is chiefly owing to the single curve of the spine 

 having its concavity anteriorly, the effect of which is to throw the 

 shoulders and head forwards, so that the weight of these organs falls j 

 in front of the vertical line passing through the joints on which the , 

 legs move. The muscles of the legs of the Quadrumana having far 

 less power than in man, they walk more feebly, and their bent figure 

 give* them the attitude which is assumed during decrepit old age in 

 the human race. If we descend further in the scale of species, we 

 find gome of the Quadrumana, such as the C'ercopithccus, furnished 

 with long tails. The tail in this order of monkeys may be considered 

 as a fifth organ of locomotion, and is of essential service in the act of 

 climbing. The strength of the tail in some species is sufficient to 

 enable the animal to suspend its solid weight to the limbs of trees, 

 leaving the hands nearly free to perform many of the offices necessary 

 in procuring food, and often to enact performances accompanied with 

 grimaces, for which many of the monkeys are remarkable. Few of 

 the monkeys below the orang-outan walk on the lower extremities 

 alone, but they move on their four arms precisely like quadrupeds, as 

 the Red Howling Monfcpy in fg. 33. The lemurs, perhaps, never 



V 



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Fig. 33. Kfd Uowlinj Monkey. 



attempt to walk erect, and they are less capable of doing so, by their 

 organisation, than the higher orders of Quadrumana. Now, although 

 the monkeys are denied the erect attitude and power of moving as 

 bipeds, like man, still they move with great facility as quadrupeds; 

 thus distributing the weight of the body on four pillars of support, 

 instead of two ; besides which, by means of their four hands, they 

 can climb trees with a facility and precision which would cause the 

 most agile school-boy to despair of outstripping them even for an 

 instant. The long arms of the gibbons enable them to pass from tree 

 to tree with wonderful rapidity, so that if they are inferior to man as 

 bipeds, they outstrip him in moving in woods of such density that 

 impediments present themselves at almost every step, and of such a 

 nature as tends to obstruct the progress of the pedestrian. Indeed 

 the conversion of the foot into a hand in these animals, instead of 

 being a sign of degradation, has been asserted by some foreign natu- 

 ralists to be no proof of inferiority in a zoological point of view ; and 

 in support of this opinion it is said that in certain districts (as the 

 Landes of Aquitaine) the peasants, who obtain their livelihood by 

 collecting the resin of the Pinna maritima, and who are termed 

 ' resiniers,' acquire a power of opposing the great toe to the others like 

 a hinder thumb ; but on this subject Professor Owen remarks, that 

 " supposing the extent of the motion of the great toe to be sufficiently 

 increased by constant habits of climbing, or in connection with a 

 congenital defect of the upper extremities, still it does not appear 

 that the os calcis (that is, the bone of the heel), or other bones of the 

 foot, have lost any of the proportions which so unerringly distinguish 

 man from the ape." Indeed, whether we turn our attention to the 

 figure of the head, the length of the arms and legs, the structure and 

 figure of the spine, or more especially to the conformation of the foot 

 or band in man, compared with those organs in the Quadrumana, we 

 see differences which at once (at least in the eye of the zoologist) 

 distinguish man from the highest of the lower animals; and, if these 

 characters are prominent in the framework, still more conspicuous are 

 the mental qualities which elevate and distinguish man far above all 

 other beings inhabiting this earth. 



The Bat. [CHEIROPTERA.] Bats present locomotive organs of a very 



IfAT. HIST. DIV. VOL. HI. 



peculiar construction. Destined like birds to move in the air, their 

 skeleton is adapted in conformity to that purpose. The bones are 

 light, the body small, the arms and fingers greatly developed, to 

 afford a great number of points for the attachment of the delicate 

 membrane of which the wing is partly composed, as may be 

 observed in the annexed figure (34) of the Short-Eared Bat. The hand 

 of the bat rotates outwards and inwards like the wing of a bird, 

 so that when the wing is folded the little finger lies on the smaller 

 bone of the fore arm. The thumb is not included in the membrane 

 of the wing, but projects beyond its margin, where it forms a hook 

 for holding objects. The four succeeding fingers support the 

 membranous wing, which when expanded presents an extensive 

 surface for striking the air during flight. The legs are small, twisted, 

 and so weak as to bs incapable of supporting the body when on the 

 ground. The toes, terminating in sharp claws, are well adapted for 

 grasping elevated objects, to which the animal suspends itself in an 

 inverted position ; by thia means it can easily launch itself into the air 

 on the slightest alarm. 



Fig. 34. 



As the bat is incapable of chasing and capturing its prey on the 

 ground, and its food is chiefly composed of insects taken on the 

 wing, it requires the attainment of a much greater velocity of move- 

 ment 'than it would be able to accomplish by means of its lower 

 extremities, were they even much stronger than they are. It has, 

 therefore, been furnished with a peculiar apparatus adapted to aerial 

 progression. The principles of its locomotion may be best studied in 

 connection with the locomotion of birds. [FLYING.] 



Quadrupeds. The movements of quadrupeds differ in principle 

 from those of bipeds, and also from those of hexapods (Insects). 



In all quadrupeds the axis of the trunk is directed more or less 

 horizontally, the angle of inclination depending chiefly oil the 

 difference between the length of the anterior and posterior extremities. 

 In some animals the giraffe, for instance the fore legs are the 

 longest, and the axis of the trunk inclines upwards ; in others, such 

 as the hare, grayhound, and especially the jerboa and kangaroo, the 

 hinder limbs preponderate in length : the axis consequently (sup- 

 posing the animal to stand with the four feet on the ground) inclines 

 anteriorly downwards. The difference between the lengths of the 

 anterior and posterior limbs produces a very sensible effect on the 

 movements of such animals. 



In quadrupeds the weight of the body is transmitted to the 

 ground by means of their four legs, but we shall find on examination 

 that they do not all bear an equal share of the burden, and that fie 

 different species present a diversity of structure which influences 

 i their movements very perceptibly. In the elephant, for example, the 

 I legs are nearly straight, a conformation which enables the animal to 

 1 support the mass of its body with the greatest mechanical advantage : 

 but, great as it is well known to be, the strength of the bones and 

 muscles of its legs is far from being in proportion to the mass of its 

 body when compared with that of many smaller quadrupeds; and 

 we consequently find that the speed of the elephant is not propor- 

 tional to its bulk. 



Quadrupeds move their four legs either singly and successively, 

 or in various orders, which correspond with the different velocities 

 of the animal. These different kinds of movement of the legs are 

 known under the terms walking, trotting, galloping, and leaping. 



As everybody is familiar with the horse, we shall select that animal 

 to illustrate the manner in which the locomotion of quadrupeds in 

 general is effected. The subject possesses more or less interest to 

 . iiici-t persons, yet of the millions of people who are in the daily 

 habit of seeing the horse in motion, how very few consider the means by 

 which the movements of that valuable animal are performed. Let us 

 suppose the horse to be standing on its four legs, as in fig. 35, number 4, 

 and that it commences the walking step by moving its left hind leg, 

 as in number 1 ; this having been advanced and placed on the ground, 

 the right fore leg is next raised and advanced, as in number 2, and having 

 been placed on the ground, the right hind leg performs a similar 

 movement, and the legs of the animal are in the position number 3 ; 

 lastly, the left fore leg is advanced, and placed in the position of 

 number 4. These four movements complete the step, and during the 

 series the centre of gravity of the animal passes over a corresponding 

 space. This is the order in which nearly all quadrupeds move their 

 legs in slow walking; but some authors do not coincide in this 

 statement, amongst whom is Borelli, who has figured the horse as 

 moving both the legs on the same side at once in walking, as some 

 horses are taught to do in the amble, and as the giraffe is known to do 

 naturally. 



It 



