Graphics Reference
In-Depth Information
shoulder blades become prominent as they rotate. The cat proceeds to stalk
its prey, keeping its profile low and head steady before coming to a halt at a
position where it judges the distance from its prey to be such that will enable
a successful chase. In anticipation of the next move, the cat bends its front
legs and draws the hind legs forward in readiness for a thrust of power that
will come from the hind legs to achieve high levels of acceleration in which to
begin the chase. At this stage the cat often twitches its shoulders and the tip
of its tail in anticipation of the chase. A sudden burst of energy takes the cat
from its slow, anticipatory movements into a full run in an instant.
Our two examples demonstrate how the change from one gait to another
may be gradual process or a sudden transformation.
The speed of a walk is determined by the length of the stride (its amplitude)
and how regularly the stride is made (its frequency). To walk more quickly, an
animal increases the frequency of the stride. Once this change has provided
the maximum return and to increase the speed even further, it is then
necessary to increase stride length. Once both the length and the speed of
stride are at their maximum, it then becomes necessary to change the gait
from a walk into a trot. To create an additional increase in speed then requires
a further change in gait to a run.
Quadrupeds
When we think of quadrupeds, we naturally imagine such animals as cats,
dogs, and horses, but it is accurate to say that not all animals with four limbs
are strictly quadrupeds. Some animals have developed forelimbs that through
evolution have become fins, wings, or arms with hands used for manipulation
or for locomotion. Those animals that have four limbs are classed as
tetrapods
,
and quadrupeds are just one of the groups that fall within this classification.
The term
quadruped
has its root in Latin, meaning
four feet
, and is used to
denote land animals that use four legs as a mode of locomotion. Mostly it
applies to mammals and reptiles.
Legs provide a very effective and efficient way of getting around on the land,
though it is not the only method. However, legs are so effective that most land
animals with legs are capable of faster travel than animals without legs, and
in very general terms those animals that have four legs are capable of higher
speeds than comparable animals with two legs.
Quadruped Anatomy
The anatomical structure of various animals serves them in different
ways, though the complexity of forms, from the simplest animal to the
most advanced, share common features based on the common needs for
locomotion, feeding, breathing, and procreation. The detailed design solutions
for all these actions are wide ranging, but they serve the common purpose.
Here we take a look at some of the structures that relate to locomotion.
