Page 60 - Mammal (DK Eyewitness)

How many toes? Shetland Soemmerring’s Brazilian
tapir
gazelle forelimb
pony forelimb
skeleton
skeleton
forelimb
skeleton
Lower arm bone Lower arm bone
The original mammals probably Wrist
walked on all four legs, on paws bones DISAPPEARING TOE
The tapir is an odd-
with five “fingers.” Today there is TWO-TOED toed hoofed mammal,
WALKING
almost every variation imaginable. The gazelles are like the horse (p. 10). Lower
Odder still is the fact
The horse, a sizable mammal, even-toed hoofed that its front feet arm
bones
mammals (p. 10),
have four toes while
walks on its tiptoes, and has only and these dainty its back ones have
one toe on each foot. Small mam- feet allow them three. The fourth toe
to run at great
is smaller than the
mals such as the shrew still have all speed. others and does not
five digits. In general, a mammal touch the ground,
except when it is
with long limbs is a swift mover; very soft.
short limbs indicate strength Palm
and perhaps digging ability. bone Wrist
Gazelles and antelopes have bones
ultraslim limbs for speed. Seals
and bats possess large, finger-
supported limb surfaces to push Wrist bones
aside water or air. Claws, nails, Finger bones
hooves, fleshy pads, and other Palm
bones
structures tip the toes. Cannon
(palm)
bone
Key to colored bones
PENTADACTYL PLAN (based on human hand)
The basic mammalian
limb ends in five digits, Lower arm bones
like our own hands and (lower leg bones)
feet. Many rodents,
primates, and carnivores Wrist bones
have kept this “penta- (ankle bones)
dactyl” design. The hoofed
mammals have lost
different digits in different Palm bones
groups. Each bone, or set (sole bones) Finger bones
of bones, in the limb is
represented by the same Finger bones
color throughout. (Names (toe bones)
in brackets refer to the
equivalent bones in the Section through SAND-SHOED
foot and lower leg.) zebra’s hoof MAMMAL
The camel, another
even-toed hoofed
INSIDE THE HOOF
The zebra’s hoof is made of Finger mammal, has enlarged,
hard, protective horn with a bone flexible foot pads
shock-absorbing pad of fat that spread its weight
(the plantar cushion) between well over the soft
it and the toe bones. desert sand.

Position
of plantar ONE-TOED WALKING
cushion The slim limb bone of the horse
has been modified by evolution
Toe bone to leave only one toe, the 3rd
(middle) or pastern (p. 13). This FLEXIBLE FEET
is joined to a long, thick cannon The dinky feet of the
bone which represents the fusing rock hyrax bear flat-
of the palm bones. The whole tened nails, not true
design does away with the hooves: four at the
numerous fingers and toes, with front, three at the back.
their heavy muscles and joints. It
combines lightness with strength,
Outer hoof especially toward the end of the
made of horn limb, giving the horse its speed.

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