26 
THE FIRST GREAT DIVISION. 
motion of the knee, is thereby shortened in equal proportion. A fatigue^ similar to 
that produced by the action of ascending, is occasioned by walking with a very wide 
step. As the legs are thereby placed considerably apart, the body sinks lower at 
the moment of their separation ; and as it is necessary to raise the body proportionally, 
when turning alternately on each leg, the fatigue is consequently greater. 
Man is not compelled to swing his arms greatly to assist his walking, except when 
confined to a very narrow path from which he cannot depart, and then he employs 
every means to correct the unsteady motion of the body. Apes always require the 
assistance of their arms in walking; and such as have these extremities longest, like 
the Orang Outang {Pithecus Satyriis)^ and the Long-armed Monkey or Gibbon 
{Vithveus ftrr), use them with the greatest advantage. 
Among Quadrupeds, the action of walking is performed in the following manner; 
The articulations of the hind-legs arc first bent slightly, and extended in order to 
carry the body forward ; in which movement the extensors of the knee and heel par- 
ticularly contribute. The breast is thrown forward by this movement, the fore-legs 
incline backwards, and the animal would certainly fall, did it not instantly throw its 
fore-legs forward in order to support itself. The trunk is dratvn upon the fore-legs, 
which are now fixed in this position, and the action of the hind-legs is again repeated. 
But it must be observed that, In the action of walking, these movements are not per- 
formed at the same instant, by the legs of each pair ; for, in that case, the animal 
would necessarily be completely suspended for a moment over the ground. Its motion 
would then no longer be a walk, but a succession of leaps, particularly denominated a 
full-gallop. On the contrary, each step is executed by t^YO legs only, one belong- 
ing to the fore pair, and the other to the hind pair. WTicn tlie motion is performed 
by the legs on the same side, it is called an amble — when by legs on opposite sides, 
a pace. 
During the amble, the body being alternately supported by two legs of the same 
side, is obliged to balance itself to the right and left, in order to avoid falling, and 
the right fore-foot moves to sustain the body, urged onwards by the right hind-foot. 
Tt is this balancing movement which renders the arable of the Horse and Ass so agree- 
able to invalids. 
In the pace, the body is supported alternately by two legs placed in a diagonal 
manner. The right fore-leg is advanced to sustain the body, thrown forward by the 
extension of the loft hind-foot ; and at the same instant the latter bends in order to 
its being moved forward. MTiile these are raised, the right hind-foot begins to extend 
itself, and the moment they touch the ground, the left; fore-foot moves forward to sup- 
port the impulse of the right foot, whicli again moves fonvard. 
Quadinipeds having the fore-feet longer than the hinder, as may be observed in tha 
Giraffe, or Ciunelupard, possess tlic chief strength of their body in the fore-legs, and 
accordingly the principal impulse is given by extending tho fore-foot. The Sloths, 
and all animals which like them have the fore-legs greatly disproportioned to tho 
others, drag themselves onwards with a laborious and tedious movement, by first 
extending the anterior legs, and then bending them so as to draw the body onward.® ; 
and witii the Slcths, tliis diiEcult motion is further increased by the imperfect articu- 
lations and general feeblcnc.ss of the hinder-legs. 
The legs of the Mammiferous Quadrupeds move forwards and backwards in planes 
nearly parallel to the spine, and not far from the middle plane of the body upon whicli 
the weight operates. On the contrary, iu the Oviparous Quadrupeds, the thighs are 
directed outwards, while the bendings of the limbs take place in planes perpendicular 
to the spine. In the latter case, the weight of the body acts with a much longer 
lever in opposing the extension of the knee. These animals, therefore, have the 
knees always bent, and the belly drags upon the ground between the legs. For this 
reason they have received the name of Reptiles. 
The short leaps of the Hares, and particularly of the Jerboas, arc occasioned 
by the great length of their hinder as compared to the fore-legs. Indeed, their fore- 
legs arc so short, that had they not the precaution to make this prancing movement, 
these animals would be thrown down by each impulse of the hind-feet. It is only in 
ascending a hill, that they can be said to walk at all. Their movement on level ground 
is performed by a succession of short leaps ; and when they attempt to walk slowly 
upon level ground, they arc compelled to move themselves by the fore-feet, and merely 
to drag the hinder pair after them. We may obaervo tho latter movement in the 
Rabbit, aiul still more distinctly in the Frog. 
The Otters, Beavers, Water Tortoises or Turtles, and other quadrupeds designed 
for swimming, have the hinder-legs placed very far apart to facilitate the motion. 
They arc, therefore, impelled laterally, the line of motion becomes crooked, and tho 
trunk is urged onwards from side to sidc- 
In Leaping, the body rises entirely from tho earth, darts into the air, and remains 
suspended for a momentary period, depending for its duration on the force of projec- 
tion. Ihis movement is performed by the sudden extension of all tho inferior arti- 
culations, after they have undergone an unusual degree of flexion. Their rapid ex- 
tension gives a violent shock to the bones composing the articulations. The impulse 
IS then communicated to the centre of gravity of the animal’s body, and it is pro- 
jected with a determined velocity depending on its weight. Aleaping body is, therc- 
tore, a projectile which gradually loses the acquired velocity by which it ascended, its 
motion being continually retarded, and finally destroyed by the force of gravity exer- 
cised by the earth. We are therefore enabled to ascertain the curve described by a 
leaping body in the air, with the time and place of its descent, when the projectile force 
and the force of gravity are given, and allowance made for the resistance of tho air. 
All the animals which leap best have the hinder-legs and thighs much longer and 
■ thicker than the antoi ior — the projectile force, and consequently the extent of the leap, 
being regulated by tlic proportional length of the muscles. Tho surprising leaps of 
the Kangaroo, Jeiboa, and Frog, arc plainly owing to this cause. 
The smaller animals leap much farther than the larger, in proportion to their size. 
This must follow obviously, if it be considered that when tho projectile force impressed 
on two bodies is in propordon to their different magnitudes, their velocity will be 
equal, and that the extent of the space through which they pass depends entirely upon 
their respective velocities. The leaps of small and large animals arc therefore nearly 
equal. 
Man and Birds are the only animals capable of leaping vertically or hopping, be- 
cause they alone have the trunk placed directly over tho legs, and tho direction of a 
leap depends upon the situation of the centre of gravity, in respect to the member by 
which the impulse is given. They are also capable of leaping forward, by impressing 
a greater degree of force on the rotatory motion of tho thigh than on that of the leg; 
or they may even leap backwards, by making an opposite exertion. On the contrary, 
Qu.*idrupcd3 can only leap forwards. 
Hunning differs from walking, only in tho body being projected forward at each 
step, and in the hinder-foot being raised before the anterior foot touches the ground. 
It consists, in fact, of a series of low leaps performed by each leg. As tho acquired 
velocity is preserved, and augmented at each bound by the new velocity thereby added 
to it, running is more rapid than the quickest walking step. An animal cannot, there- 
fore, stop itself instantaneously when running, though a stop may be made at each 
step in walking. In leaping forward, a previous run is advantageous, because it acids 
the momentum acquired during the run to that obtained from tho leap itself; but a 
vertical leap or hop would be entirely prevented by a run, or at least consider- 
ably diminished. For this reason, a horse in full gallop, preparing to leap, 
retards his velocity before making the spring. In running, an animal inclines 
its body forwards, that the centre of gravity may be in a proper situation for re- 
ceiving an impulse in that direction from tho Iiind«r-leg. It is also requisite 
to move the fore-leg rapidly forward to guard against falling. Were any obstacle to 
inten’cne, so as to prevent this leg from reaching the ground in time to support the 
body, a fall would be the consequence. It also follows, lliat interruptions of this 
kind are more dangerous in running than in walking, on account of the greater momen- 
tum of the body, and for the same reason they occur more frequently. lilan never 
varies his manner of running, except in taking longer or shorter steps, or in giving 
to his body a greater or less degree of velocity ; but Quadrupeds vary their mode 
of running, by tho different order in which they raise each foot, or bring it to the 
ground. 
The feet diagonally opposite rise simultaneously in the trot, and fall at once, each 
pair alternately, but in such a manner, that for a moment all the four feet arc off tlm 
ground. The sound of tho animal’s steps are therefore heard two and two in succes- 
sion, and a regular motion is produced. 
The Dog, Hare, and many other quadrupeds, can only run in the manner particu- 
larly denominated the full gallop, which is the most rajiid motion of tho Horse. These 
animals raise the anterior feet at each stop; the body is projected forwards by the 
extension of the bind-feet; the two fore-feet descend at the same lime, and are 
followed by the two hind-feet also descending together. By this means, the step* 
of the horse are hc^d by two beats at a time, differing in this respect from the 
common gallop, ulicre the two fuie-fcet are lifted unequally, and fall one after another, 
and from those other varieties of the gallop, where the horse’s footsteps arc licard by 
a series of three or four beats, from the hinder-feet falling to tho ground either both 
together or one after the other. 
Many animals leap by organs different from feet, hut they all agree in this respect, 
that the movement is occasioned by the sudden extension of several articulations. 
Serpents leap by foliUng their bodies into several undulations, which are unbent at 
the same instant, according to the degree of velocity wliich they wish to impart to 
their bodies. Only a few genera are assisted in this motion by the scales of the bcHy* 
which they are able to derate and depress at pleasure. Some Fishes leap to the tops 
of cataracts by bending tliclr bodies strongly, and then unbending them suddenly, so 
that they rise with an elastic and powerful spring. 
Several animals, which in reality leap, have been improperly said to fly. 'The 
Flying Lemurs, Flying Squirrels, ami Flying Phalangers, have membranes between 
the feet, but their toes arc not elongated. These membranes serve to support them 
for some time in the air, and enable them to take great leaps in descending ; but tim 
membrane acts merely as a parachute, as these animals camiot raise themselves in tb® 
air. In the same manner, the Flying Dragon, a small lizard found in the East Indit‘5» 
supports itself for some moments during a leap, by a membrane sustained by a 
bony rays, articulated to the spine of the back. 
5Ian and various other animals possess the power of seizing objects, by surroun^l' 
ing and grasping them with their fingers. For this reason, it is necessary that the 
fingers should he separate, free, flexible, and of a certain length. Man has such 
fingers cn his hand only; but Apes and some other kinds of animals have them both 
on the hands and feet; hence they arc termed quadruviana, or four-handed. 
Man surpasses all other animals in the delicate operations wliich his hand is capable 
of performing. The Apes and Lemurs alone possess with him a thumb opposable to the 
other fingers, and forming with them a kind of forceps. They are consequently the 
only animals capable of holding moveable objects in a single hand. But it is 
pcnsable to perfect prehension that they should have tho power of rotating tlm 
upon the fore-am, and the bones of the shoulder must be placed so as to prevent the 
scapula or shoulder-blade from being thrown forwards. 
The Squirrel, Opossum, Rat, aud other animals, possess fingers sufficiently siwJ' 
and aexiblo to enable thorn to take up objects, but they can only hold them by 
iissistanea of both paws. Dogs and Cats, which have the toes shorter, and bosWe® 
arc under the necessity of resting on their foro-foct, can retain their hold of 
stances solely by fixing them upon tho ground with their paws. Those animaU 
the toes united and drawn together under the skin, or enveloped in horny hoofs, at'-’ 
incapable of cxercisiug any prehensile power. 
Climbing is greatly facilitated by a power of seizing and grasping firmly* 11^** 
but an indifferent climber, because he can only grasp with hU hands. His ftn’t 
chiefly adapted for supporting the body, and afford but an imperfect moans of 
it by the extension of the knees and heels. The arms form, therefore, the ’ 
means of drawing the body upwards in climbing. 
Aloiikcys, and other Quadrumana, are the best climbers. They can seize equ^ ^ 
well with their four extremities ; and the position of their hind-fo'A is still 
favorable to this action, as the soles arc turned inwards, instead of being dircc 
outwards. Aut-eators and Sloths have a considerable protuberance on tho 
which nearly accomplislics the same end ; and with the Opossums and Phalaug 
