ANATOMY OF THE FROG:
The body structure, or anatomy, of the frog is very similar to the anatomy
of man. Both man and the frog have the same kinds of organs and systems
of organs. The frog's anatomy, however, is much simpler.
General Body Features
As in other higher vertebrates, the frog body may be divided into a ___________________
__ ______________. The flat head contains the brain, mouth,
eyes, ears, and nose. A short, almost rigid neck permits only limited
head movement. The stubby trunk forms walls for a single body cavity,
the coelom. Man's internal organs are housed in one of three distinct
hollow cavities--the chest, the abdomen, and the pelvis. The human chest
is separated from the abdomen by a powerful muscular partition, the diaphragm.
There is no such partition in the frog's coelom. All the frog's internal
organs--including the heart, the lungs, and all organs of digestion--are
held in this single hollow space.
The Skeleton and Muscles
The frog's body is supported and protected by a bony framework called
the skeleton. ____________, except for an expanded area that encases
the ____________. Only _________ _____________ make up
the frog's backbone, or vertebral column. The human backbone has 24 vertebrae.
The frog ____________.The frog does not have a tail. Only a spikelike
bone, the urostyle, remains as evidence that primitive frogs probably
had tails. The ____________
____________ is a downward extension of the vertebral column. The
shoulders and front legs of the frog are somewhat similar to man's shoulders
and arms. The frog has one __________
________________. Man has two forearm bones, the radius and the ulna.
Both frog and man have one ___________________________. The hind
legs of the frog are highly specialized for leaping. The single ________________________. Man
has two lower leg bones, the tibia and the fibula. In man and in the
frog, the ____________ is the single upper leg (thigh) bone. A
third division of the frog's leg consists of two elongated anklebones,
or tarsals. These are the ___________________________. The astragalus
corresponds to the human talus. The calcaneusin the human skeleton is
the heel bone. As in other vertebrates, the frog skeleton is moved by
muscles. Skeleton-moving muscles are made of skeletal, or ___________________.
Internal organs contain smooth muscle tissue.
The Circulatory System
The frog heart is the only organ contained within the coelom which has
its own protective covering. This is the ____________. There are
two upper chambers of the heart, ___________ _________________________. The
frog heart, however, has only one lower chamber, _______ ____________ In
man, the lower heart chamber is divided into two compartments, the
right ventricle and the left ventricle. Oxygen-rich blood and oxygen-poor
containing waste gases are present together in the frog ventricle at
all times. The oxygenated and oxygen-poor bloods, however, do not mix.
Such mixing is prevented by a unique arrangement of the frog's heart.
Instead of "perching" on top of the ventricle, the right atrium
dips downward into the ventricle. This causes oxygen-poor blood entering
the right atrium to pass all the way down to the bottom of the ventricle.
Meanwhile, oxygenated blood is received by the left atrium and enters
the same single ventricle. The pool of oxygen-poor blood at the bottom
of the ventricle holds up the oxygenated blood and prevents it from sinking
to the bottom. When the oxygen-poor blood flows from the ventricle into
vessels leading to the lungs, the oxygenated blood tries to "follow" it.
The lung vessels, however, are filled with oxygen-poor blood, blocking
the oxygen-laden blood and forcing oxygenated blood to detour into
the arteries. These carry the oxygenated blood to the tissues. Frog
has both a solid and a liquid portion. The liquid plasma carries solid
elements such as red blood cells and white blood cells.
The Skin and Respiratory System
The frog is covered by a soft, thin, moist skin composed of two layers, _______________ _________________.
The skin does not merely protect the frog but ____________________An
extensive network of blood vessels runs throughout the frog's skin. Oxygen
can pass through the membranous skin, thereby entering directly into
the blood. When a frog submerges beneath the water, all its respiration
takes place through the skin. Oxygen is obtained directly from the water.
The frog does not breathe through its skin alone. Adult frogs have paired,
simple, ___________ As in man, air enters the body through two
nostrils, passes through the windpipe, and is received by the lungs.
The mechanism of breathing, however, is different in the frog from that
in man. In humans breathing is aided by the ribs, the diaphragm, and
the chest muscles. The frog has no ribs or diaphragm, and its chest muscles
are not involved in breathing. ___________ ____________________________________________________________.
However, it may also breathe with its mouth closed. The floor of the
mouth is lowered, causing the frog's throat to "puff out." When
the nostrils open, air enters the enlarged mouth. Then, with nostrils
closed, the air in the mouth is forced into the lungs by contraction
of the floor of the mouth.
The Digestive and Excretory Systems
The frog's mouth is where digestion begins. It is equipped with feeble,
practically ______ _______These are present only in the
upper jaw. The frog's ____________ is highly specialized. Normally,
the tip of its tongue is folded backward toward the throat. From this
position the frog can flick it out rapidly to grasp any passing prey.
To better hold this prey, the tongue is sticky. Food passes from the
frog's mouth into the stomach by way of the __________. From the ____________ the
food moves into the _____________________, where most of the digestion
occurs. Large digestive glands, the liver and the pancreas, are attached
to the digestive system by ducts. A gall bladder is also present. Liquid
wastes from the kidneys travel by way of the ureters to the urinary bladder.
Solid wastes from the ________________ pass into the ____________.
Both liquid and solid waste material leave the body by way of the cloaca
and the cloacal vent.
The Nervous System and Sense Organs
The frog has a __________________ nervous system. It consists
of a ____________________ ____________ The important
parts of the frog brain correspond to comparable parts in the human brain.
The ____________ regulates automatic functions such as
digestion and respiration. Body posture and muscular co-ordination are
controlled by the ____________. The ____________ is very
small in the frog. By comparison the human cerebrum is very large. In
man the cerebrum is involved in many important life processes. Only _____________________ originate
in the frog's brain. Man has 12. Similarly, the frog has only ______________________.
Man has 30 pairs. Two simple holes make up the nostrils for the frog.
There are complex valves but no long nasal passages as there are in man.
The frog's sense of smell is registered by olfactory lobes. These make
up the forward portion of the brain. The eye is crude. Its fixed lens
cannot change its focus. Poorly developed eyelids do not move. To close
its eye, the frog draws the organ into its socket.________________________________________________________
____________________ There is no external ear. Both eardrums, or
tympanic membranes, are exposed. There is only one bone in the frog's
middle ear. The human middle ear contains three bones (ossicles). As
in man, semicircular canals help to maintain body balance. Life Cycle
of a Frog
True Love? When Frogs mate, the male frog tends to clasp the female underneath
in an embrace called ____________ He literally climbs on her
back, reaches his arms around her "waist", either just in
front of the hind legs, just behind the front legs, or even around
the head. Amplexus
can last several days! Usually, it occurs in the water, though some
species, like the bufos on the right mate on land or even in trees!
While in some
cases, complicated courting behavior occurs before mating, many species
of frogs are known for attempting to mate with anything that moves
which isn't small enough to eat!
While in the amplexus position, the male frog fertilizes the eggs as
they get are laid. _________ ___________________________,
whereas_______________________________________. Some frogs
leave after this point, but others stick around to watch over the little
ones. Some have very unusual ways of caring for their young.
Frogs and Toads tend to lay many many eggs because there are many hazards
between fertalization and full grown frogness! Those eggs that die tend
to turn white or opaque. The lucky ones that actually manage to hatch
still start out on a journey of many perils. Life starts right as the
central yolk splits in two. It then divides into four, then eight, etc.-
until it looks a bit like a rasberry inside a jello cup. Soon, the embryo
starts to look more and more like a tadpole, getting longer and moving
about in it's egg. Usually, about 6-21 days (average!) after being fertilized,
the egg will hatch. Most eggs are found in calm or static waters, to
prevent getting too rumbled about in infancy! Some frogs, like the Coast
foam-nest treefrog, actually mate in treebranches overlooking static
bonds and streams. Their egg masses form large cocoon-like foamy masses.
The foam sometimes cakes dry in the sun, protecting the inside moisture.
When the rain comes along, after developement of 7 to 9 days, the foam
drips down, dropping tiny tadpoles into the river or pond below.
Shortly _________________, the tadpole still feeds on the remaining
yolk, which is actually in its gut! The tadpole at this point consists
of ___________________________________________. It's really
fragile at this point. They usually will stick themselves to floating
weeds or grasses in the water using little sticky organs between its'
mouth and belly area. Then, 7 to 10 days after the tadpole has hatched,
it will begin to swim around and feed on algae. After about 4 weeks,
the gills start getting grown over by skin, until they eventually disappear.
The tadpoles get teeny tiny teeth which help them grate food turning
it into soupy oxygenated particles. They have long coiled guts that help
them digest as much nutrients from their meadger diets as possible. By
the fourth week, tadpoles can actually be fairly social creatures. Some
even interact and school like fish!
Tadpole with legs
After about_____________________________ start to sprout. The
head becomes more distinct and the body elongates. By now the diet may
grow to include larger items like dead insects and even plants. The arms
will begin to bulge where they will eventually pop out, elbow first.
After about 9 weeks, the tadpole looks more like a teeny frog with a
really long tail. It is now well on it's way to being almost full grown!
Young Frog, or Froglet By ____________, the tadpole
has only a teeny tail stub and looks like a __________________ _______________.
Soon, it will leave the water, only to return again to laymore eggs and
start the process all over again!
By between ________________, depending on water and food supply,
the frog has completed the ____________________. Some frogs
that live in higher altitudes or in colder places might take a whole
to go through the tadpole stage...others may have unique development
stages that vary from your "traditional" tadpole-in-the-water
type life cycle. Now these frogs will start the whole process again...finding
mates and creating new froggies.