Support
Bony Fish in Water
Terrestrial tetrapedal (4 limbed) mammal on Land
properties of water (density similar to
protoplasm of cells) which make support
Air (density much lower than protoplasm of cells)
provides little buoyancy:
easier (1)
-
-
density of water (800 times more than
air) offers buoyancy (1) / less energy to
deal with support
swim-bladder to adjust depth / its position
in water by adjusting the amount of gas in
the swim bladder (1)
 - for buoyancy providing
(hence only little fin movement to
air does not offer much support due to its low
density (1)
skeleton support against gravity (1) by:
- 4 limbs act as struts (weight-bearing poles) (1)
to support and lift the body against gravity (1)
with tendency of limbs immediately beneath the
body and as straight as possible
The straighter of the limbs during lifting the body off the
ground, the higher is their efficiency. Hence, with
tendency:
1. of limbs immediately beneath the body and as straight
as possible
maintain itself at a constant depth
or to change its depth)
legs projected laterally from body in primitive
amphibian
- wasteful of energy in lifting body off the ground by
muscular effort (requires to spend much of their
muscular energy to hold the trunk off the ground)
modern reptilian intermediate between amphibian
and mammals
legs project straight down from beneath the body in
mammalian
- This can raise the body well clear off the
ground.
Body is supported directly by bones of four
limbs. (This type of stance can save energy by
transmitting the weight along the straight struts)
- Less muscular effort in lifting is required
2. some evolved into dipedal to release forelimbs for
developing manipulative skills e.g feeding, building,
cleaning…etc.
-
vertebral column / backbone acts as a
cantilever bridge which bridges the gap between
the limbs offers support to the body / skeletons
act as lever (1) to support the body against
gravity
Bony Fish in Water
Propulsion resistance of water (1) overcome by
1. streamlined body (1) and laterally
compressed body
 - reduce drag to minimum for
forward movement
- counteract the lateral drag
1. slimy scales / slimy surface (1)
(slimy secretion from oil glands)
 reduce friction with water
reaction of water provides propulsion
Alternate contraction and relaxation of
antagonistic myotomes (myo = muscle, tom
= to cut; muscle blocks, for power) along
the vertebral column (endoskeleton, for
framework) on both side of the body results
in forward propulsion and move in any
direction.
Side-to side movement of body thrusting against
surrounding water during swimming:
- the forward component of the reaction force is
responsible for the forward movement of the
fish through the water
the sideway component (the lateral drag) will tend to
swing the tail and the head towards opposite
directions but is not very pronounced
forward thrust generated by
- tail movement caused by alternate
contraction of muscles (1) on either side
of body
1. series of waves travel towards the
tail from the anterior end of the fish;
or
2. side-to-side lashing of tail and
caudal fin
3. elongated body with high flexibility
and highly developed myotomes
 increase efficiency of propulsive
mechanism and speed of
swimming
-
tail fin: increases surface area for
pushing against_water_(1)
to stop (paired pectoral fins)
for steering (paired pectoral and pelvic fins)
Terrestrial tetrapedal (4 limbed) mammal on Land
Jointed bony skeleton together with antagonistic
striated muscle pairs ( flexor and extensor) function
as lever system.
action of antagonistic muscles of limbs (1) :
extensor and flexor of limb work antagonistically (1)
to provides efforts which are transmitted through
tendons (tough, non-contractile and relatively
inextensible) to move limbs backwards and forwards
(1) in walking
Limbs thrust on the ground.
Foot presses downwards and backwards against the
ground, resulting in an equal and opposite force
which is transmitted along the length of the limb:
- vertical component
 lifting body off the ground(1) to reduce friction
with the ground (1)
- horizontal component
 propel the body forward
Efficiency of movement
- the limbs project straight down from beneath the
body. Body is supported directly by bones of
four limbs. Less muscular effort in lifting is
required during locomotion
More powerful and musclular hind legs
- provide main propulsive force for forward
movement
Other adaptations (e.g .for fast speed and
powerful running in horse)
- lengthened limbs
- elongation of lower leg sections
- upperleg angles inward
- low degree of weight in the legs
- upper legs with huge muscles
- unguligrade 蹄行性 (ungula = hoof, grad =
step) locomotion with special gait (步態 / 步式)
that only hoofs (蹄) covered tips of digits touch
the ground
Stability
Bony Fish in Water
water current and moving through water
creates water turbulence which upsets
stability.(1).
Terrestrial tetrapedal (4 limbed) mammal on Land
Stability and pattern of locomotion
1. when the mammal is not moving:
centre of gravity within the area bounded by the
4 legs
fish overcomes turbulence with various
fins and the laterally flattened body:
1. yawing by vertical fins (dorsal and
ventral fins) (1) and laterally flattened
body (1) /massiveness of head
2. pitching by paired fins (pectoral and
pelvic fins) (1) / horizontal fins
3. rolling by all fins [dorsal and ventral
fins / vertical fins (1) and horizontal /
paired fins (1)] and the laterally
compressed body
sensory inputs from lateral line (1) to help
maintaining balance
2. when the mammal moves:
to prevent toppling (1) when moving:
lifting of limbs causes the animal to topple (1) as
CG is off-centred, overcome by:
- before the one foot off the ground, centre of
gravity moves to the a triangular area bounded
by the 3 legs that remain touching the ground
-
usually move in diagonal pattern (1):
left-hind
left-fore
right-hind
right-fore
 shift of centre of gravity away from
moving leg (1) and ,hence, centre of
gravity always inside the triangular area
bounded by the legs in contact with
ground (1)
role of eye, inner ear and proprioceptors in muscles
and cerebellum in maintaining coordinated balance
(2):
sensory inputs from eye / inner ear / proprioceptors
in muscles (1) and coordinated by cerebellum (1) to
help maintaining balance
Comparison of the means of support between aquatic and terrestrial vertebrates
Aquatic vertebrates (fishes)
Terrestrial vertebrates (tetrapods)
Body weight support by buoyancy of water with the
swim bladder
Body weight supported by limbs with strong
muscles
No limbs and strong muscles necessary
strong limb bones and limb muscles necessary
Almost no energy required for support
Large amount of energy required for support
Visceral skeleton mainly as gill arches to support
Visceral skeleton reduced and contributing to the
the gills
formation of jaws and larynx
Appendages in form of fin rays
Appendages in form of pentadactyl limbs
Neither pectoral nor pelvic girdle (if present)
connected with vertebral column
Both pectoral and pelvic girdle connected with
vertebral column
2005 –II- 8
. 生活在水中和陸地生境的動物，利用不同機制以應付運動的各種要求，這包括支持、推進和穩
定。硬骨魚和陸生四足哺乳動物在牠們不同的生存介質中如何應付這些要求？試比較牠們的異
同。（ 20 分）
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